INTRODUCTION

Background

The structure and function of the myocardium of the heart have challenged and perplexed anatomists since the adoption of anatomy as a proper science five centuries ago (Buckberg et al., 2001; Buckberg, 2006). Throughout this period, a seemingly endless search for the final link between the form and function of the myocardium was conducted.   Eventually, the nature of this missing link was "unraveled," much like the helical ventricular myocardial band (HVMB) itself.  Considering how long it took science to understand this macroscopic arrangement of the myocardium, a compelling argument can be made that the discovery of the HVMB by Francisco Torrent-Guasp has been one of the most critical anatomical discoveries of the last century.  At its core, Torrent-Guasp's discovery sheds a powerful light on one of the most puzzling anatomical features of the human body.

Perhaps James Bell Pettigrew (1832-1908), a Scottish anatomist and physiologist, best described the frustrating relationship anatomists shared with the structure of the myocardium when we wrote in 1864, concerning the myocardial arrangement: "An arrangement so unusual and perplexing that it has long been considered as forming a kind of Gordian knot of anatomy.  Of the complexity of the arrangement, I need not speak further than to say that Vesalius, Haller, and De Blainville confessed their inability to unravel it" (Torrent-Guasp et al., 2001).  Pettigrew's reference to other great investigators of the myocardial arrangement should not be overlooked. It is a testament to the work of anatomists who struggled with this "Gordian Knot of Anatomy" long before Francisco Torrent-Guasp discovered the HVMB.  Although the work of many anatomists and investigators was important to Torrent-Guasp's eventual discovery of the HVMB, there are a few whose work cannot go unmentioned.

In the 17th century, anatomy was still in its infancy, and its practitioners were primarily concerned with the anatomical properties of the soul.  However, a Danish anatomist named Niels Stenson, better known as Nicolaus Steno (1638-1687) helped refine anatomy into the science it is today.  During his lifetime, Steno endeavored to shift anatomical priority from the metaphysical realm to a practice rooted in exploring and understanding the practical body (Arikha, 2006).  While Steno spent much of his time dissecting the brain, he also had a great interest in muscular physiology.  His fascination with muscle contractility included an interest in the muscular architecture of the heart.  In 1663, Steno wrote to a colleague about the arrangement of muscle fibers in the heart, "…they are different from some of the others, only in that they do not run straight but, where they go down obliquely from the base towards the apex, they return upwards" (Kardel, 1994). Nicolaus Steno's observation regarding the direction of myocardial fibers began an inquiry into the structure of the myocardium that would take centuries to resolve and culminate in the discovery of the HVMB.

In the 19th and early 20th centuries, three anatomists contributed significantly to the discovery of the helical ventricular band.  These included American anatomist Franklin P. Mall, his protégé John Bruce MacCallum, and the previously mentioned James Bell Pettigrew of Scotland.

In 1864, James Bell Pettigrew published an essential article in the saga of the HVMB, entitled: ‘On the Arrangement of the Muscular Fibers in the Ventricles of the Vertebrate Heart, with Physiological Remarks’ (Pettigrew,1864). In this article, Pettigrew described the arrangement of fibers he observed while dissecting the ventricles of fish, reptiles, birds, and mammals.  Concerning mammals, including humans, Pettigrew determined that the left and right ventricles each comprised seven distinct muscle fiber layers:  three "external" layers, an "intermediate" fourth layer, and three "internal" layers.  Furthermore, these layers were defined by a marked change in the direction of their constituent muscle fibers (Pettigrew,1864).

In his report, Pettigrew also described the relationship and interplay between the fiber layers of the left and right ventricles.  Pettigrew carefully reported on the direction he observed for each layer.  In a general sense, he explained the three external fiber layers as extending from base to apex in a left-to-right spiral across the anterior aspect of the heart.  Pettigrew then illustrated the fourth intermediate layer as a circular layer.  Finally, he observed the three internal fiber layers running from apex to base in a right-to-left spiral across the posterior aspect of the heart (Pettigrew, 1864).

Although decades later, Torrent-Guasp's discovery of the HVMB did not place great significance on the seven individual layers described by Pettigrew, his work was not ignored.  The macroscopic observations Pettigrew had made concerning the general directionality of the external and internal fiber groups would be helpful in Torrent-Guasp's eventual unwinding of the HVMB.  Pettigrew also believed that the fibers of both ventricles were essentially continuous and that their arrangement accounted for the powerful, rolling movement of the ventricles (Pettigrew, 1864). His belief in the constant nature of the muscle fibers and their impact on the contractility of the ventricles would be verified through the work of Torrent-Guasp.

In 1911, Franklin P. Mall published an article entitled ‘On the Muscular Architecture of the Ventricles of the Human Heart’, which was a comprehensive review and continuation of the work his protégé John Bruce MacCallum had conducted (Mall, 1911).  The article demonstrated a noticeable shift in how anatomists were beginning to look at the structure of the myocardium.  Instead of viewing the myocardium in terms of its fiber layers as Pettigrew had, Mall and MacCallum attempted to examine the heart muscle as a whole (Mall, 1911).

Mall and MacCallum took a different approach in their analysis of the myocardium, focusing on fiber bundles that could be seen running in various directions throughout the ventricles.  These bundles seemed to provide a type of scaffolding that gave structural support to the ventricular walls.  Mall's article goes to great lengths to describe the pathways these bundles travel as they emerge from the fibrous rings at the base of the heart and are tucked away into the apex.

Mall and MacCallum came close to the complete unwinding of the ventricular band.  Mall described a method by which the pig's heart could be unrolled beginning from the left ventricle.  He included a sketch that depicted an "unrolled" pig heart.  Unfortunately, MacCallum's method for unrolling pig hearts was backward, starting with the left ventricle (Mall, 1911). Their technique was a miss for the unveiling of the HVMB.  Had they refined their dissection techniques and attempted to unroll the right ventricle first instead of the left, they might have discovered the HVMB for themselves. Perhaps the most impressive aspect of the report were the beautiful illustrations of the myocardial fibers, sketched initially by MacCallum (Mall, 1911) and replicated here (Figs 1-3).

Figure 1. “Drawing of pig heart (MacCallum’s method), apical view: Demonstrating - two vortices (arrows), superficial bulbo-spiral (A) and superficial sinu-spiral (B) bundles, Right (RV) and Left (LV) ventricles, and demonstrating - pulmonary trunk (PT).” Adapted from “On the Muscular Architecture of the Ventricles of the Human Heart” by Franklin P. Mall, 1911: Am J Anat 11(3): p. 221. Color drawing rendition by Dr. Jorge Alfredo Orsi

Figure 2. “Drawing of Pig heart: Left view, opened dilated left ventricle; Bulbo-spiral band lining the interventricular septum”. Adapted from “On the Muscular Architecture of the Ventricles of the Human Heart” by Franklin P. Mall, 1911: Am J Anat 11(3): p. 250. Color drawing rendition by Dr. Jorge Alfredo Orsi.

Figure 3. “Unwrapped pig heart, demonstrating muscle fiber orientation of the cylinder from the aorta to the pulmonary trunk”. Adapted from “On the Muscular Architecture of the Ventricles of the Human Heart,” by Franklin P. Mall in 1911. Color drawing rendition by Dr. Jorge Alfredo Orsi.

In 1954, Francisco (Paco) Torrent-Guasp, a medical student at Salamanca University near Madrid, Spain, became interested in the structure and function of the heart, a curiosity to which he would dedicate his life.  Specifically, Torrent-Guasp was interested in the mechanism of ventricular contraction and blood flow through the organ's chambers.  Since the 17th century, philosophers and scientists alike had failed to discover the comprehensive myocardial structure that accounted for cardiac motion and the necessary movement of blood in and out of the heart.  Torrent-Guasp decided to pursue this elusive mechanism (Ross, 2006).

When Torrent-Guasp began his inquiry into the heart's musculature, anatomists, physiologists, and physicians had primarily abandoned their attempts at untangling the ventricular myocardium.  With technological advancements and the emergence of cardiac surgery, many researchers moved beyond their concern with general structure and began exploring more finite aspects of the heart (Ross, 2006).  In an uncharacteristic move, the scientific community seemed willing to allow the macroscopic organization of the myocardium to remain a mystery.  With the exciting new work in surgical correction of cardiac defects, toiling away working on a centuries-old anatomical puzzle did not seem worthwhile.  This type of anatomical research appeared to be a step backward.

At the beginning of his experimentation, Torrent-Guasp turned to the microscope to find a clue that would unlock the entire ventricular mass; it quickly proved unproductive.  Torrent-Guasp began to examine the heart muscle as a whole, tracing the pathways of the muscular fibers, as Mall and MacCallum had done previously (Aguilar, 2005). This new approach led to Torrent-Guasp's initial dissections of the heart muscle, in which he carefully pulled apart layers of muscle beginning at the apex.  As he would with all his dissections of the heart, he used only blunt instruments and primarily his fingers.  These original apex-to-base dissections revealed a "figure-of-eight" pattern of myocardium that appeared to swirl around the apex. Not knowing what this figure-of-eight arrangement meant, Torrent-Guasp reversed his dissection path to a base-to-apex direction (Ross, 2006), resulting in his complete unwinding of the heart muscle in 1973.

Francisco Torrent-Guasp had managed to unravel the ventricular myocardium completely, from the pulmonary trunk to the aorta, exposing the previously unknown organization and structure of the heart muscle. He demonstrated that the ventricular mass was a single band of muscle wrapped in a double helical coil that encapsulated two completely connected but utterly separate ventricles (Aguilar, 2005). The Gordian Knot of anatomy had been undone.

Although Torrent-Guasp had ended a century of anatomical wonderment and frustration, no one in his native Spain seemed interested.  While he had undoubtedly made a significant anatomical discovery, Torrent-Guasp had only exposed the heart's form; he now needed to address its function.  This would prove difficult, and it would take nearly 30 years for Torrent-Guasp to develop a comprehensive and reasonable relationship between the HVMB and the innate movements of the heart (Aguilar, 2005). The HVMB provides a framework for understanding the heart as a complex, three-dimensional structure rather than a simple pump.  This enhanced understanding can potentially revolutionize the diagnosis and treatment of cardiovascular diseases.

Understanding the helical ventricular myocardial band (HVMB) is crucial for treating heart diseases, especially when surgically correcting congenital and acquired defects. Procedures that involve cutting or removing parts of the ventricles directly affect HVMB function. Historically, these surgeries were performed without fully understanding their long-term impact on the heart's muscular structure. Current research focuses on mitigating complications caused by surgical disruption of the HVMB, with clinicians working to refine techniques and improve patient outcomes. Conditions such as complete and congenitally corrected transposition of the great arteries, Ebstein's Anomaly, and Tetralogy of Fallot necessitate this detailed understanding (Carrio et al., 2010; Corno et al., 2006, 2007). This research seeks to document the historical origins and evolving understanding of the helical ventricular myocardial band (HVMB) and produce a plastinated series of bovine hearts illustrating its sequential unwinding, effectively preserving its structural transformations.

MATERIALS AND METHODS

Preparation  

Mature bovine hearts (15) were used for each dissection of the HVMB.  The hearts were acquired from a local slaughterhouse and refrigerated until their dissection.  The dissections were performed according to Francisco Torrent-Guasp's method (Kocica et al., 2006). The dissection technique demonstrated by Torrent-Guasp is available through YouTube and can be viewed by following the hyperlink: The Helical Heart.

Each heart was initially boiled in water for approximately two hours to soften the surrounding superficial fat and connective tissue. Then, the hearts were allowed to cool overnight before being cleaned. Using fingers and a blunt dissection tool, superficial fat, vessels, and epicardium were scraped away from the surface of the heart.  Both right and left atrial appendages were removed with a scalpel.  After removing the great vessels, approximately 2-3 cm segments of the aorta and the pulmonary trunk were preserved. If the cleaned hearts were not immediately dissected, they were stored with refrigeration until the day of dissection. The specimens were acclimated to room temperature prior to dissection.

 Dissection 

The HVMB was thoroughly dissected through manual manipulation with fingers and the assistance of a blunt dissection instrument. First, the trunks of the pulmonary artery and the ascending aorta were bluntly separated.  Next, the thin layer of superficial fibers that spans the paraconal/anterior interventricular sulcus was cut with a scalpel. The right ventricle-free wall was ready to be opened by placing a finger deep inside the pulmonary trunk and pulling apically.  Because of the size of the bovine heart, a significant amount of force was required to open the right ventricular free wall. Preventing damage to the pulmonary artery trunk was crucial throughout the process.

Following the initial detachment of the right ventricular free wall from the septum, the right ventricular cavity was further exposed by pulling toward the right margin of the heart toward the apex, following the exact orientation of the myocardial fibers.  By pulling in this direction, the posterior wall of the right ventricular cavity was exposed, and the interventricular septum became visible.  By detaching the myocardium following the path of the fibers in the direction of the apex, it was seen that the muscle continued around the posterior aspect of the heart toward the free wall of the left ventricle and onto the base of the aorta.  The section of myocardium dissected to this point (from the pulmonary trunk, around the atrioventricular sulcus aspect of the heart, and continuing to the root of the aorta) was the basal loop of the HVMB.  Portions of the ascending and descending segments of the apical loop that make up the central fold of the HVMB were now visible.

At this point in the dissection, it was necessary to return to the interventricular border of the right ventricular cavity.  From this position, two distinct bands of muscle were identified crossing one another (Fig. 7).  The vertically-oriented superficial band of muscle was the ascending segment, and the more bottomless, horizontally-oriented band was the descending segment of the apical loop.  These muscular segments each had attachment points in the right fibrous trigone at the base of the aorta that must be detached (Kocica et al., 2007).

Detaching the aorta was the next and most challenging step in the dissection of the HVMB.  The aorta was most strongly held anterior to the left ventricle by its attachments to the cardiac skeleton's left and right fibrous trigones.  Additionally, a weaker attachment to the aortic annulus helps to anchor the aorta (Kocica et al., 2006).  Cutting these three points of attachment detaches the aorta from the left ventricle.  The aorta was pulled away from the left ventricle in the direction of the muscular fibers of the ascending segment of the HVMB to which the aorta was still attached.  Continuing to unravel the ascending segment of the HVMB following the patterns of the myocardial fibers revealed the left ventricular cavity.

The final steps of HVMB dissection involved completely unraveling the muscle into one continuous straight myocardial band.  The first step in this final process was unraveling the remainder of the apical loop with a simple 90-degree turn around the apex.  Finally, a 180-degree turn around the remaining central fold completed the dissection (Fig. 8).  This final turn revealed the entirely undone HVMB of Francisco Torrent-Guasp, a continuous band of myocardium capped on one end by the trunk of the pulmonary artery and on the opposite end by the aorta. In this case, multiple bovine hearts were dissected to various degrees to be plastinated and displayed sequentially to better illustrate the structural nature of the HVMB.

Plastination

Several bovine hearts, prepared to demonstrate the sequential unwinding of the HVMB band for display and educational purposes, were ready for plastination using the cold silicone method (von Hagens, 1985, 1986; Henry et al., 2019).

Following dissection, hearts were held in 10% formalin to prevent decay and increase the soft myocardium's rigidity.  The dissected hearts remained in formalin until dissection was completed.  After dissection, hearts were placed in a solution of hydrogen peroxide (3%) and ethanol (50%) in water for 24 hours.  This preparatory solution removes chemicals (e.g., formalin, etc.) that could interfere with plastination.  Additionally, this solution bleaches the myocardium and enhances the visibility of myocardial fibers. The hearts were then washed in running tap water for 24-48 hours in preparation for dehydration.

Dehydration

The hearts were dehydrated in the cold (-25^o C) 100% acetone.  Acetone purity was measured using an acetonometer (Biodur®) and recorded. The acetone bath was changed weekly until acetone purity remained above 99%.  After dehydration, the containers of acetone with the hearts were brought to room temperature to remove residual fat.

Impregnation        

After dehydration/defatting, the specimens were submerged in an impregnation mix (100:1) of silicone (NCS10) and catalyst (NCS3) (Silicone Inc., High Point, NC, USA) inside a vacuum chamber (Henry et al., 2019). The vacuum chamber was kept at -15^oC throughout impregnation.  Over 4 weeks, the pressure within the chamber gradually decreased from 760 mmHg to 5 mmHg.

Curing         

After impregnation, the hearts were removed from the silicone mixture and drained inside the freezer for 48 hours and at room temperature for an additional 7 days. At this point, the hearts were manipulated and placed into the desired positions for their final presentation and curing. The hearts were exposed to a cross-linker (NCS6) (Silicone Inc., High Point, NC, USA) over 3-7 days. The hearts gradually hardened and maintained their final presentation.

RESULTS

The bovine hearts, collected at the slaughterhouse, dissected bluntly, sequentially, and plastinated, all demonstrated various essential portions of the HVMB after unraveling the heart. The dissected, plastinated hearts were evaluated, and eight were considered appropriate for display.  These specimens illustrate the various stages of the unwinding of the band (HVMB) from the beginning (pulmonary trunk) to the end (ascending aorta) (Figs. 4-11).  The typical architecture of the heart was preserved with marked differentiation of the ventricular walls.

Figure 4. Apical view of transverse section of a plastinated bovine heart (Specimen 1): Right (RV) and left (LV) ventricles, interventricular septum (IS), free margin of the right ventricle with the initial cleavage of the overlapping myocardium forming the superficial myocardial band (arrow).	Figure 5. Right view of the apical portion of the plastinated bovine heart (Specimen 2): Note the evident detachment of the superficial myocardial layer of both the right (RV) and left ventricles (LV) from the deep layer of the left myocardium. The deep layer forms the bulk of the left ventricle. The cleavage of the overlapping myocardium forms this superficial band.	Figure 6. The left view of the initial unwrapping of the **HVMB (right segment) basal loop of a bovine heart (Specimen 3) demonstrates the left ventricular (LV) fiber architecture surrounding its lumen. The apical loop (AL) is incompletely separated from the superficial band (star). The right ventricular (RV) free wall is displaced to the left. The right ventricular fibers are unraveling from the left ventricular fibers.
Figure 7. Basal view of the helical overlapping path of subepicardial fibers (SF) at the basal region of the bovine ventricles (Specimen 4). The pulmonary trunk (P) and right ventricular fibers are partially detached from the aorta (A). Lumina: Right (*) and Left (**) ventricles.	Figure 8. Left view of the HVMB progressive unfolding at the posterior interventricular cleavage (Specimen 5) at the subserosal/posterior interventricular sulcus. The right deep ventricular free wall supports the pulmonary trunk (PT), and its tricuspid valve is observed. The descending (Ds) and ascending (As) segments of the left ventricular wall are seen, with the ascending segment connected to the aorta (A).

The band's identifiable beginning (pulmonary trunk) and end (aorta) were prominent.  As the myocardium was unwound, the right ventricular structures (tricuspid valve, papillary muscle, chordae tendineae, etc.) were revealed (Figs. 8, 9).  As more of the band was freed and unwound, the interventricular septum, basal and apical portions of the band, and more of the free wall of the right ventricle are seen, revealing the descending and ascending segments of the muscular band.

The early stages of the myocardial band unraveling progress is characterized by the separation of the right and left ventricular myocardium. Figure 4 illustrates the initial cleavage of the overlapping myocardium, marking the onset of myocardial band detachment. As the process progresses, the superficial layer of the myocardial band begins to separate from the deeper layers (Fig 5). This separation is particularly evident in the right ventricle, where the anterior/cranial free margin demonstrates the initial cleavage of the overlapping myocardium.

The HVMB contains two loops, the basal and the apical loop, each composed of two separate segments. A central 180° myocardial fold divides and connects the two loops of the HVMB. Subsequent stages involve the progressive unfolding of the myocardial band. Figure 6 provides a caudal view of the initial unwrapping of the right segment of the basal loop of the right ventricular myocardial band (HVMB). This process reveals the complex architecture of the left ventricular fibers, including the apical loop and the superficial band. The right ventricular fibers gradually peel away from the left ventricular band fibers as the unwrapping continues.

The helical arrangement of myocardial fibers is the key finding in this study. Figure 7 showcases the helical overlapping path of subepicardial fibers in the basal region of the bovine ventricles. This helical organization contributes to the heart's intricate three-dimensional structure and plays a crucial role in its pumping function.

In the final stages of the HVMB unfolding process, the distinct segments of the left ventricular wall become apparent (Figures 9-11). The descending and ascending segments, which originate from the pulmonary trunk and aorta, can be observed. These segments intertwine to form the complex three-dimensional structure of the left ventricle.

Figure 9. (Specimen 6) Left view of the final stage of the HVMB progressively unfolding into a single band. From left to right: pulmonary trunk (PT) and right ventricle (RV); continuing as left ventricular structures: descending (Ds) and ascending (As) segments of the left ventricular wall; ascending aorta (A). The HVMB band can be followed from the pulmonary trunk to the aorta. In the four-chamber section, the descending segment reveals the inner surface of the left ventricle and is surrounded by the ascending segment. This specimen shows that the left ventricular myocardium is not a homogeneous structure but is formed by different overlapping ventricular segments that constitute the myocardial wall.	Figure 10 (Specimen 7): Left lateral view showcasing the fully unfolded helical ventricular myocardial band (HVMB). The continuous myocardial band is visualized from the pulmonary trunk (PT) and right ventricle (RV) to the ascending aorta (A), encompassing the left ventricular descending (Ds) and ascending (As) segments. The four-chamber section reinforces the segmental organization of the left ventricular myocardium.	Figure 11 (Specimen 8): Final left-view stage of the helical ventricular myocardial band (HVMB) unfolding. The progression from the pulmonary trunk (PT) and right ventricle (RV) to the ascending aorta (A) via left ventricular descending (Ds) and ascending (As) segments is shown. The four-chamber view confirms the left ventricle's layered, non-homogeneous structure.

DISCUSSION

This study and literature review thoroughly examine the myocardial band, a complex three-dimensional cardiac structure. The dissection, analysis, and plastination of bovine hearts yielded valuable insights regarding the formation and function of this essential anatomical structure.

Bovine hearts are significantly larger than human hearts, making them easier to dissect and study. This larger size allows researchers to visualize and analyze the complex muscular structure of the HVMB more readily. While there are differences, bovine hearts share certain anatomical and physiological similarities with human hearts. This makes them a valuable model for studying general cardiac mechanics.

While this study offers valuable insights into the myocardial band, we acknowledge the limitations of the dissection and preparation techniques. The myocardial band's fragility often results in tissue damage and fragmentation.  Plastination proved useful for displaying Torrent-Guasp's helical ventricular myocardial band (HVMB) in a series of unwinding bovine hearts. The resulting rigidity of the plastinated specimens facilitated a simultaneous demonstration of the unwinding steps. However, several hearts were unsuitable and were discarded. Only 8 of the initial 15 specimens survived the process. A disadvantage of the Torrent-Guasp technique is the production of brittle specimens. It is hypothesized that the loss of collagen due to boiling diminishes specimen flexibility, thereby contributing to the observed fragmentation in the final winding stage. Despite these challenges, visualizing the spiral myocardium at various unwinding stages proved beneficial. It allowed observation of the entire myocardial fiber path from its origin in the pulmonary trunk to its termination in the aorta.

The simplicity of Torrent-Guasp's method for unwinding the myocardial band is striking, especially considering the centuries of anatomical investigation that preceded it. Using primarily blunt dissection with his hands, Torrent-Guasp penetrated the ventricular mass, following the natural direction of the muscle fibers. The HVMB continues to intrigue with its simple structure and complex function (Buckberg et al., 2001; Kocica et al., 2006; 2007; Torrent-Guasp et al., 2005; Jouk et al., 2007).

Before discovering the HVMB, the interventricular septum was believed to reside entirely within the left ventricle. This is incorrect, as myocardial fibers from both ventricles contribute to its formation. With the discovery of the HVMB, the origin of the interventricular septum has been revised, and its muscular composition has been divided into three strata (right, middle, and left) based on myocardial fiber directionality (Kocica et al., 2006, 2007).

Understanding the HVMB's anatomical and physiological properties is clinically relevant for treating heart diseases, particularly in the surgical correction of certain congenital and non-congenital heart defects. Procedures requiring cutting or re-sectioning a portion of either ventricle impact the HVMB's physiological function. Until recently, such procedures were performed without sufficient knowledge of their post-operative effects on HVMB structure and function. There is a concentrated effort to understand the potential complications arising from surgical disruption of HVMB anatomy. Clinicians also strive to refine these procedures to minimize the impact on the heart's muscular architecture and improve patient outcomes following these complex operations (Carrio et al., 2010). These defects include ventriculo-arterial discordance (complete transposition of the great arteries), double discordance (congenitally corrected transposition of the great arteries), Ebstein's Anomaly, and Tetralogy of Fallot (Corno et al., 2006, 2007).

While the fundamental concept of the helical ventricular myocardial band (HVMB) applies to both bovine and human hearts, there are important similarities and differences. Both species observe the basic principle of the ventricular myocardium being organized in a helical structure. The general concept of the heart muscle forming a continuous band with a complex, spiraling arrangement is consistent.

The bovine heart is significantly larger than the human heart, which affects the relative proportions and dimensions of the HVMB. There are also variations in the precise orientation and arrangement of the muscle fibers. Bovine and human hearts have different heart rates and hemodynamic characteristics, influencing how the HVMB functions. A standard dissection technique can successfully dissect helical fibers in human and other species' hearts while retaining the segmentation of the myocardium. No anatomic differences were found between bovine, porcine, and human hearts (Montes, 2020).

This study's dissection-based demonstration of the Torrent-Guasp myocardial arrangement, while simple and compelling, serves as a foundation for understanding complex ventricular interactions. Contemporary research, employing techniques beyond dissection, offers both supporting and conflicting perspectives. For instance, Lukenheimer et al. (2006) used histological analysis of myocardial cell orientations to describe the left ventricular architecture, while Yuan et al. (2011) utilized diffusion tensor magnetic resonance imaging (DT-MRI) to reconstruct myocardial fiber architecture, observing a helical functional band consistent with dissection findings. Conversely, Hoffman (2017) argues that the Torrent-Guasp model, despite its explanatory power, overlooks critical anatomical aspects, particularly the lack of anatomical basis for non-parallel fiber bands. Hoffman's critique highlights the model's limitations in explaining varied helical angles, the origin of subepicardial and subendocardial fibers, the role of circumferential fibers, and the interconnectedness of myocardial fibers. Furthermore, the model's exclusion of circumferential fibers in the septum contradicts histological and DT-MRI evidence. These diverse findings underscore the ongoing debate and the need for a comprehensive model that integrates various imaging and histological data.

A sequence of plastinated unwinding myocardium specimens is now part of the permanent collection at the DiDio & Goldblatt Interactive Museum of Anatomy and Pathology in the College of Medicine and Life Sciences at the University of Toledo.

Acknowledgments

 The author would like to acknowledge Dr. Jorge Alfredo Orsi's invaluable contributions. His masterful rendition of the drawings from the original publication of Mall 1911 brought the historical source material to life with exceptional clarity and detail. Dr. Orsi's dedication to this project is deeply appreciated.