What is Dr. Zubair Khalid's research focus?

Dr. Zubair Khalid specializes in molecular virology, mRNA vaccine development, and computational biology, with a focus on avian pathogens like IBDV and Avian Reovirus.

Where is Dr. Zubair Khalid currently working?

Dr. Zubair Khalid is a Postdoctoral Research Associate at the University of Maryland (UMD), specifically within the Department of Animal and Avian Sciences.

Grooves of the Heart: Coronary and Interventricular Sulci

Name: Grooves of the Heart: Coronary and Interventricular Sulci
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-20

The grooves of the heart are the visible surface furrows that separate the atria from the ventricles and the two ventricles from each other. The coronary sulcus (also called the atrioventricular groove) circles the heart between the atria and ventricles, while the interventricular sulci, named the paraconal and subsinuosal grooves in dogs and cats, run obliquely across the ventricular mass and mark the position of the interventricular septum deep beneath them.

These grooves are not decorative. They are the highways of the coronary circulation. The major coronary arteries and cardiac veins run inside them, cushioned by epicardial fat, and their positions are the landmarks surgeons, cardiologists, and anatomists use to find vessels, place ligatures, and interpret imaging. Understanding the grooves means understanding where the heart's blood supply lives.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

What a Sulcus Is and Why the Heart Has Them

A sulcus (plural: sulci) is a groove or furrow on an organ's surface. On the heart, sulci form where the outer wall of one chamber meets another and where the surface dips inward slightly along an internal partition. The heart is not a smooth sphere. It is a folded, twisted muscular pump with four chambers arranged so that the atria sit at the base and the ventricles form the apex. Where those chambers meet, the surface shows a groove.

Two features create these grooves. First, the atria are thinner-walled and sit like a cap on the ventricles, so the transition creates a visible indentation. Second, the interventricular septum, the muscular wall dividing the left and right ventricles, reaches the heart's surface at two lines, and the epicardium dips along those lines. The grooves are external landmarks. The septum is the internal wall. They are related but not the same structure, and confusing the two is one of the most common errors in cardiac anatomy.

The grooves carry fat and vessels. In most domestic mammals, the coronary sulcus and the interventricular sulci are filled with subepicardial fat that surrounds the coronary arteries and veins. In the dromedary camel, for example, subepicardial fat covers the heart base, the coronary groove, and both longitudinal interventricular grooves, and this fat has a relatively low density on CT imaging compared with the myocardium [1]. That fat is not inert padding. It protects the vessels from compression during the cardiac cycle and provides a dissection plane for surgeons.

The Coronary Sulcus (Atrioventricular Groove)

The coronary sulcus is the ring-like groove that separates the atria above from the ventricles below. It is also called the atrioventricular groove because it marks the level of the atrioventricular valves internally. The right and left atria sit above this groove, and the right and left ventricles sit below it.

The coronary sulcus is not a perfect circle. It is distorted by the great vessels entering and leaving the heart base, and it is deeper on the left side where the left atrium and left ventricle meet. The groove contains the main trunks of the coronary arteries and the coronary sinus with its tributaries.

In the horse, the coronary sinus and great cardiac vein run within the coronary groove, and their anatomy has direct clinical importance because catheterization of these structures is increasingly used for arrhythmia diagnosis and treatment [2]. A postmortem study of 64 adult warmblood equine hearts measured the coronary sinus and great cardiac vein within the coronary groove and found a mean combined length of 240 mm (standard deviation 36 mm) in the groove [2]. The same study showed that the great cardiac vein's distance to left atrial myocardium changed dramatically along its course, from a median of 10 mm near the coronary sinus end to 2 mm at the mid-left free wall and then to 32 mm at the paraconal interventricular sulcus [2]. That kind of millimeter-level data matters when a catheter is being advanced through the groove.

The coronary sinus itself is a venous channel that collects most of the heart's venous blood and delivers it to the right atrium. In dogs, the coronary sinus has been characterized directly, with a study of 32 hearts showing that its length in dogs under 10 kg averaged 18.49 mm with a diameter of 4.40 mm, and that its shape was cylindrical in half the cases and funnel-shaped in about a third [3]. The same study measured the great cardiac vein at the level of the paraconal interventricular sulcus in dogs weighing 20 to 29 kg and found a diameter of 2.13 mm there, widening to 4.03 mm distally [3]. These numbers show that the groove is not a uniform tube. Vessel caliber changes along its length.

An important anatomical principle is that the coronary sinus is normally located in the left atrioventricular sulcus, inferior to the wall of the morphologically left atrium [4]. This normal position is so consistent that when a coronary sinus-like channel appears in the right atrioventricular sulcus, it signals a major developmental anomaly. One reported fetal specimen with congenitally corrected transposition had a venous channel receiving most coronary veins located in the right atrioventricular sulcus, inferior to the right atrium, with mirror-imaged venous drainage [4]. That case illustrates how tightly the groove and its contents are linked to normal cardiac situs.

The Interventricular Sulci: Paraconal and Subsinuosal

The interventricular sulci are the two grooves on the ventricular surface that mark where the interventricular septum meets the epicardium. In dogs and cats, these are named the paraconal interventricular sulcus and the subsinuosal interventricular sulcus. In humans and in much of the human medical literature, the equivalent grooves are called the anterior interventricular sulcus and the posterior interventricular sulcus. The names differ because the orientation of the heart in the thorax differs between species, and veterinary anatomists chose terms based on the dog's cardiac position rather than the human's.

Paraconal Interventricular Sulcus

The paraconal interventricular sulcus runs obliquely down the cranioventral surface of the ventricles, from near the coronary sulcus toward the apex. It corresponds to the anterior interventricular sulcus of human anatomy. The paraconal groove carries the paraconal interventricular branch of the left coronary artery, which is the veterinary equivalent of the left anterior descending artery, and the great cardiac vein.

In the horse, the great cardiac vein's relationship to surrounding myocardium changes as it approaches the paraconal interventricular sulcus, with the distance to left atrial myocardium increasing to a median of 32 mm at that point [2]. This is a useful landmark during electrophysiology procedures because the vein is farther from atrial tissue there than it is along the mid-left free wall.

Subsinuosal Interventricular Sulcus

The subsinuosal interventricular sulcus runs down the caudodorsal surface of the ventricles, from the coronary sulcus toward the apex, and corresponds to the posterior interventricular sulcus in human terminology. It carries the subsinuosal interventricular branch, which in most domestic mammals arises from the right coronary artery.

In fetal pigs, the subsinuosal (posterior) interventricular sulcus branch always arose from the right coronary artery, and the circumflex artery rarely extended to the posterior interventricular sulcus [5]. This is more consistent than in humans, where the arterial supply to the posterior interventricular sulcus is variable. The same study found that other branches, including the acute marginal branch, obtuse marginal branch, and sinoatrial nodal artery, were not significantly different between fetal pigs and humans, and that coronary dominance patterns were also similar [5].

In xenarthrans (armadillos, sloths, and anteaters), the right coronary artery typically emits a subsinuosal interventricular branch, present in 94.9 percent of specimens studied [6]. That branch runs in the subsinuosal groove just as it does in dogs and pigs, showing that the groove-vessel relationship is deeply conserved across mammals even when other details vary.

What Runs Inside the Grooves

The grooves are the conduits for the coronary circulation. The table below summarizes the major grooves, their contents, and species notes.

Groove	Location	Primary Contents	Species Notes
Coronary sulcus (atrioventricular groove)	Circles heart between atria and ventricles	Right and left coronary arteries, coronary sinus, great cardiac vein, circumflex arteries	Prominent in ruminants and horses. In horses, coronary sinus and great cardiac vein run here with a mean combined length of 240 mm [2].
Paraconal interventricular sulcus	Cranioventral surface of ventricles	Paraconal interventricular artery (equivalent to human LAD), great cardiac vein	Named paraconal in dogs and cats. In horses, great cardiac vein is 32 mm from left atrial myocardium here [2]. In dogs, great cardiac vein diameter at this groove is 2.13 mm in 20 to 29 kg dogs [3].
Subsinuosal interventricular sulcus	Caudodorsal surface of ventricles	Subsinuosal interventricular artery (equivalent to human posterior descending artery)	Named subsinuosal in dogs and cats. In fetal pigs, this branch always arises from the right coronary artery [5]. In xenarthrans, present in 94.9 percent of specimens [6].
Anterior interventricular sulcus (human term)	Anterior surface	Left anterior descending artery, great cardiac vein	Same structure as paraconal groove in dogs and cats. Used as a surgical landmark for LAD ligation in mice [7].
Posterior interventricular sulcus (human term)	Posterior surface	Posterior descending artery, middle cardiac vein	Same structure as subsinuosal groove in dogs and cats. In quail, middle cardiac vein ascends along this sulcus to the right atrium [8].

The coronary arteries themselves are highly variable in their branching patterns, but their relationship to the grooves is constant. In a study of 221 human hearts, the right coronary artery ended between the crux cordis and the left margin in 75.6 percent of specimens, and the posterior interventricular artery reached the inferior third, apex, or anterior interventricular sulcus in 67.4 percent of cases [9]. In pigs, the left coronary artery bifurcated into the anterior interventricular artery and circumflex artery in 79 percent of cases and trifurcated in 21 percent, and the anterior interventricular artery reached the apex in 79.7 percent of hearts [10]. The circumflex artery in pigs never reached the posterior interventricular sulcus [10]. These patterns show that while the grooves are fixed landmarks, the vessels inside them vary by species and individual.

Comparative Species Notes

Dogs and Cats

In dogs and cats, the interventricular grooves are the paraconal and subsinuosal sulci. The paraconal groove runs on the cranioventral surface and the subsinuosal groove on the caudodorsal surface. This naming reflects the orientation of the canine heart in the thorax, which is more upright than the human heart. The coronary sulcus is well defined and carries the main coronary trunks and the coronary sinus. In dogs, the coronary sinus has been directly characterized, with a study of 32 hearts showing that an arteriovenous trigone was present in 93.8 percent of hearts and that the left marginal vein originated mainly in the lower third of the left margin in 46.9 percent of cases [3]. The great cardiac vein runs in the paraconal interventricular sulcus, and its diameter there was 2.13 mm in dogs weighing 20 to 29 kg [3].

Horses and Ruminants

In horses and ruminants, the coronary groove is prominent and often filled with substantial subepicardial fat. In the dromedary camel, CT imaging shows the coronary groove and both interventricular grooves clearly, with subepicardial fat covering the heart base and these grooves [1]. The camel's grooves are named the left longitudinal interventricular groove (paraconal) and the right longitudinal interventricular groove (subsinuosal), following the same naming convention as dogs [1].

In horses, the coronary groove has direct clinical relevance for electrophysiology. The coronary sinus and great cardiac vein run within it, and catheterization of these structures is used for arrhythmia diagnosis and treatment [2]. The right atrial myocardial sleeve extends 52 mm (standard deviation 18 mm) into the great cardiac vein in 63 of 64 horses studied, and histology showed myocardial connections between the sleeve and left atrial myocardium [2]. These findings matter because they help explain how electrical signals can travel between the atria and the coronary venous system.

Pigs

Pigs are important comparative models because their coronary anatomy resembles the human pattern more than dogs or horses do. In fetal pigs, the posterior interventricular sulcus branch always arose from the right coronary artery, and the circumflex artery rarely extended to the posterior interventricular sulcus [5]. This is more consistent than in humans, where the posterior interventricular artery can arise from the right coronary, the left circumflex, or both. Coronary dominance in fetal pigs was similar to humans, and other branches showed no significant differences [5]. The left coronary artery in pigs bifurcates into the anterior interventricular artery and circumflex artery in 79 percent of cases [10]. An anastomosis between the terminal branches of the anterior interventricular artery and the posterior interventricular artery was found in 7.6 percent of pig hearts [10].

Birds

The quail heart shows a different coronary pattern. The major coronary arteries are the right and left septal arteries, which branch from the right and left coronary stems respectively. The right septal artery runs posteriorly and penetrates the ventricular free wall, while the left septal artery runs anteriorly and does the same [8]. The right and left circumflex arteries are directed posteriorly along the atrioventricular sulci [8]. The cardiac veins consist of three major tributaries: the middle, great, and anterior cardiac veins. The middle cardiac vein ascends along the posterior interventricular sulcus and empties into the right atrium, while the great cardiac vein runs along the anterior interventricular sulcus [8]. This shows that the groove-vessel relationship is not limited to mammals.

The Grooves as Surgical and Clinical Landmarks

The grooves are not just anatomy. They are working landmarks.

In mouse models of myocardial infarction, the anterior interventricular sulcus is now used as a guiding landmark for ligation of the left anterior descending coronary artery. The sulcus is a shallow surface groove directly visible under the microscope, with the LAD running immediately beneath it, and it provides a more stable reference than the left atrial appendage, which is often difficult to identify during surgery [7]. This change improves consistency between operators and reduces variability in ligation site [7].

In human cardiac imaging, the peri-crux cordis area is delineated using the posterior interatrial sulcus, posterior interventricular sulcus, and the left and right posterior atrioventricular grooves on the diaphragmatic surface of the heart [11]. A study of 1,006 patients undergoing coronary CT angiography used these landmarks to identify eight coronary artery distribution patterns in the peri-crux area, including four right-dominant types, one left-dominant type, and three balanced types [11]. This kind of classification depends entirely on the grooves being visible and consistent.

The grooves also appear in congenital heart disease imaging. In a study of cinematic rendering for complex congenital heart defects, the assessability of the anterior interventricular sulcus was one of the categories evaluated by pediatric cardiac surgeons, and cinematic rendering scored significantly better than traditional volume rendering in seven of nine categories [12]. The sulcus is a surgical landmark that must be seen clearly before an operation.

In horses, the coronary groove is the target for coronary sinus catheterization. The great cardiac vein's distance to left atrial myocardium changes from 10 mm near the coronary sinus to 2 mm at the mid-left free wall and 32 mm at the paraconal interventricular sulcus [2]. A catheter that is safe in one part of the groove may be dangerous in another because of these changing relationships.

Clinical Relevance, Limitations and Common Mistakes

The most common mistake is confusing a sulcus with a septum. The interventricular sulci are external grooves. The interventricular septum is the internal muscular wall. They are related because the septum reaches the surface at the sulci, but they are not the same structure. A surgeon who mistakes a groove for a septum, or vice versa, can make an incision in the wrong place.

Another common mistake is assuming that the groove names are universal. In dogs and cats, the grooves are paraconal and subsinuosal. In humans, they are anterior and posterior interventricular. In horses and ruminants, the coronary groove is prominent and the interventricular grooves follow the same paraconal and subsinuosal naming as dogs. A veterinary student reading a human anatomy text must translate the names.

A third mistake is assuming that the vessels inside the grooves are constant. They are not. In humans, the posterior interventricular sulcus can be supplied by the right coronary artery, the left circumflex artery, or the left anterior descending artery, and a study of 356 coronary CT angiograms found 25 different irrigation patterns [13]. In that study, the most frequent pattern (31.3 percent) had the basal and mid-ventricular segments perfused by a single branch from the right coronary artery at the crux, with the apical segment perfused by the LAD traveling beyond the notch of the cardiac apex [13]. Circulation was right dominant in 87.1 percent, left dominant in 9.5 percent, and balanced in 3.4 percent of cases [13]. These numbers show that while the groove is a fixed landmark, the vessel inside it is not.

A fourth mistake is ignoring the fat. The subepicardial fat in the grooves is not incidental. It protects the vessels and provides a dissection plane. In the camel, this fat is visible on CT and covers the heart base, coronary groove, and both interventricular grooves [1]. In dogs, the arteriovenous trigone is present in 93.8 percent of hearts and has a closed configuration in 60 percent of cases [3]. These details matter during surgery.

Limitations exist. Individual variation in coronary anatomy is significant, and the studies cited here describe populations, not individuals. A vessel that runs in a groove in most dogs may run outside it in a particular patient. Imaging and direct visualization remain necessary before any procedure. This article is educational and is not a substitute for veterinary diagnosis or treatment. Any specific case needs a veterinarian.

Frequently Asked Questions

What is the coronary sulcus?

The coronary sulcus is the groove that circles the heart between the atria and the ventricles. It is also called the atrioventricular groove. It contains the main coronary arteries and the coronary sinus.

What are the paraconal and subsinuosal sulci?

They are the two interventricular grooves on the surface of the heart in dogs and cats. The paraconal sulcus runs on the cranioventral surface, and the subsinuosal sulcus runs on the caudodorsal surface. They correspond to the anterior and posterior interventricular sulci in humans.

Do the grooves contain blood vessels?

Yes. The coronary arteries and cardiac veins run inside the grooves, surrounded by subepicardial fat. The paraconal groove carries the paraconal interventricular artery and the great cardiac vein. The subsinuosal groove carries the subsinuosal interventricular artery.

Are the grooves the same as the septum?

No. The grooves are external surface landmarks. The septum is the internal muscular wall between the ventricles. The grooves mark where the septum reaches the heart's surface, but they are not the septum itself.

Why are the groove names different in dogs and humans?

The names reflect the orientation of the heart in the thorax. The canine heart sits more upright than the human heart, so veterinary anatomists named the grooves paraconal and subsinuosal rather than anterior and posterior.

Which species have a prominent coronary groove?

Horses and ruminants have a prominent coronary groove, often filled with substantial subepicardial fat. In the dromedary camel, the coronary groove and both interventricular grooves are clearly visible on CT imaging.

Can the vessels inside the grooves vary between animals?

Yes. Coronary artery branching patterns vary significantly between species and between individuals. In humans, a study of 356 coronary CT angiograms found 25 different patterns of blood supply to the posterior interventricular sulcus.

Why do veterinarians care about these grooves?

The grooves are surgical and clinical landmarks. They help surgeons find coronary vessels, place ligatures, and interpret imaging. In horses, the coronary groove is the target for coronary sinus catheterization during electrophysiology procedures.