Coronary arteries: the LAD, circumflex and right coronary artery that feed the heart

The coronary arteries supply blood to the myocardium and the other tissues of the heart. The two main vessels arise from the first part of the aorta, just above the aortic valve, and the larger branches run in the grooves (sulci) on the outer surface of the heart. (OpenStax Anatomy and Physiology 2e, 19.1: Heart Anatomy.)

Their openings lie in the aortic sinuses (sinuses of Valsalva), the small pockets behind the cusps of the aortic valve, immediately above the valve. The left coronary artery comes from the left aortic sinus and the right coronary artery from the right one. (TeachMeAnatomy: Arterial Supply and Venous Drainage of the Heart.)

Unlike most organs, the heart receives most of its blood flow while it is relaxed. Coronary flow peaks when the heart muscle relaxes and nearly stops while it contracts. (OpenStax Anatomy and Physiology 2e, 19.1: Heart Anatomy.)

This is why a fast heart rate matters in coronary disease: exercise shortens diastole, the relaxation phase, which leaves less time for blood to get past a narrowed artery. The result is the chest pain of angina. (TeachMeAnatomy: Arterial Supply and Venous Drainage of the Heart.)

The left main coronary artery (LMCA, left main stem) arises from the left aortic sinus. It is short, about 5 to 10 mm long, and passes to the left behind the pulmonary trunk before it divides. (Radiopaedia: Left main coronary artery.)

It usually bifurcates into the left anterior descending artery and the left circumflex artery. In about 15% of people it trifurcates instead, giving a third branch, the ramus intermedius, which arises between the LAD and the circumflex. (Radiopaedia: Left main coronary artery.)

Through these branches the left coronary artery supplies the left atrium, the left ventricle, the interventricular septum and the atrioventricular bundles of the conduction system. (TeachMeAnatomy: Arterial Supply and Venous Drainage of the Heart.)

The LAD is one of the two terminal branches of the left main coronary artery. It runs down the front of the heart in the anterior interventricular groove (sulcus), the groove that marks the septum between the right and left ventricles, towards the apex. Its anatomical name is the anterior interventricular artery. (Radiopaedia: Left anterior descending artery.)

The LAD has two kinds of branch. Diagonal branches run to the left across the front and side (anterolateral) wall of the left ventricle and are numbered in order: the first diagonal (D1), the second (D2) and so on. Septal perforator branches dive backwards into the interventricular septum. (Radiopaedia: Left anterior descending artery.)

The LAD supplies the anterolateral wall of the left ventricle, the apex and, through its septal branches, the anterior two-thirds of the interventricular septum. Radiologists divide it into a proximal segment (origin to the first diagonal), a mid segment (first diagonal to halfway to the apex) and a distal segment. (Radiopaedia: Left anterior descending artery.)

Its length varies. A short LAD (type I) may stop before the apex; in type II the apex is shared with the RCA; in type III the LAD supplies the whole apex; and a long type IV LAD wraps around the apex and supplies more than a quarter of the inferior wall near it. This explains why an LAD blockage can damage the inferior part of the apex (the inferoapical region) as well as the front of the heart. (Radiopaedia: Left anterior descending artery.)

The LAD is the most commonly blocked coronary artery. A blockage near its origin is nicknamed the 'widow-maker' because it can cause sudden death, and because the LAD supplies the septum, its occlusion can also disturb the bundle branches of the conduction system. (Radiopaedia: Left anterior descending artery.)

The left circumflex artery (LCx, often just 'the circumflex') is the other terminal branch of the left main coronary artery. It curves to the left and backwards in the left atrioventricular groove, between the left atrium and the left ventricle, lying in the epicardium. (Radiopaedia: Left circumflex artery.)

Its main branches are up to three obtuse marginal branches, which run down the left (obtuse) margin of the heart, and it may give a left posterolateral branch. These branches supply the lateral and posterolateral walls of the left ventricle. (Radiopaedia: Left circumflex artery.)

In OpenStax's description the circumflex follows the coronary sulcus to the left and eventually meets small branches of the right coronary artery. (OpenStax Anatomy and Physiology 2e, 19.1: Heart Anatomy.)

Variants include a circumflex that arises directly from the left aortic sinus with no left main stem, and an aberrant circumflex arising from the right aortic sinus. In a left-dominant heart, the circumflex supplies the posterior interventricular artery. (Radiopaedia: Left circumflex artery.)

RCA stands for right coronary artery. It arises from the right aortic sinus (right sinus of Valsalva), runs down and to the right behind the pulmonary trunk and under the right atrial appendage (auricle), then follows the right atrioventricular groove around the right side of the heart to its inferior surface and the posterior interventricular groove. (Radiopaedia: Right coronary artery.)

In order, its branches are: the conus artery to the outflow tract of the right ventricle (from the RCA in about 60%), atrial branches including the sinoatrial nodal artery, right ventricular branches and the acute marginal arteries along the sharp lower right margin, and finally the posterior descending artery, the atrioventricular nodal artery and posterior left ventricular branches, which supply the inferior wall of the left ventricle. (Radiopaedia: Right coronary artery.)

TeachMeAnatomy summarises its territory as the right atrium, the sinoatrial and atrioventricular nodes, the right ventricle (through the right marginal artery, which also reaches the apex) and the posterior part of the interventricular septum. (TeachMeAnatomy: Arterial Supply and Venous Drainage of the Heart.)

OpenStax adds that the RCA distributes blood to the right atrium, portions of both ventricles and the conduction system of the heart. (OpenStax Anatomy and Physiology 2e, 19.1: Heart Anatomy.)

The posterior interventricular artery, also called the posterior descending artery (PDA), runs in the posterior (inferior) interventricular groove on the diaphragmatic surface of the heart, the counterpart of the LAD on the front. (Radiopaedia: Posterior descending artery.)

Its posterior septal perforating branches supply the posterior one-third of the interventricular septum, and the artery also supplies the diaphragmatic (inferior) part of the left ventricle. Near the apex and through septal branches it can connect with the LAD. (Radiopaedia: Posterior descending artery.)

Whichever artery gives rise to the PDA defines the coronary dominance of the heart. In most people it comes from the RCA. (Radiopaedia: Coronary arterial dominance.)

Coronary dominance is defined by the vessel that gives rise to the posterior descending artery. In a right-dominant heart the RCA supplies the PDA; in a left-dominant heart the left circumflex does; in a co-dominant heart a single or doubled PDA is supplied by both the RCA and the left system. (Radiopaedia: Coronary arterial dominance.)

Radiopaedia's dominance article gives about 85% right dominant, 8% left dominant and 7% co-dominant. (Radiopaedia: Coronary arterial dominance.)

Other figures differ. Radiopaedia's right coronary artery article gives about 70% right dominant, 20% co-dominant and 10% left dominant, and its circumflex article says up to 20% of hearts may be left dominant. (Radiopaedia: Right coronary artery.)

TeachMeAnatomy puts it more simply: the RCA gives rise to the posterior interventricular artery in about 80 to 85% of people, and in about 20 to 25% the circumflex branch of the left coronary artery contributes to it. (TeachMeAnatomy: Arterial Supply and Venous Drainage of the Heart.)

The sinoatrial (SA) node, the heart's natural pacemaker, is supplied by the small sinoatrial nodal artery. The standard description is that it comes from the right coronary artery in 60% of people and from the left coronary artery in 40%. In a CT study of 516 arteries, 53.4% arose from the RCA and 43% from the left circumflex artery. (Radiopaedia: Sinoatrial nodal artery.)

The atrioventricular (AV) node is supplied by the atrioventricular nodal artery. It most often arises from the distal right coronary artery, less often from the posterior descending artery or the distal circumflex, so its origin follows the dominance pattern. It usually runs through the inferior pyramidal space at the back of the heart and ends in the AV node near the central fibrous body. (Radiopaedia: Atrioventricular nodal artery.)

TeachMeAnatomy lists both nodes in the territory of the RCA. The same artery usually supplies the inferior wall, and ECG changes in the inferior leads (II, III and aVF) during a heart attack point to the RCA. (TeachMeAnatomy: Arterial Supply and Venous Drainage of the Heart.)

The main coronary vessels lie in the sulci of the heart. The deep coronary sulcus, also called the atrioventricular sulcus, runs around the heart between the atria above and the ventricles below. The anterior and posterior interventricular sulci run down the front and back between the two ventricles. (OpenStax Anatomy and Physiology 2e, 19.1: Heart Anatomy.)

The RCA and the circumflex run in the coronary (atrioventricular) sulcus, the RCA on the right and the circumflex on the left. The LAD runs in the anterior interventricular groove, and, in a right-dominant heart, the RCA turns at the crux on the back of the heart to become the posterior descending artery. (Radiopaedia: Coronary arteries.)

The apex is the pointed lower tip of the heart. It lies just to the left of the sternum between the junctions of the fourth and fifth ribs with their costal cartilages. (OpenStax Anatomy and Physiology 2e, 19.1: Heart Anatomy.)

The apex is usually supplied by the LAD. A short LAD may stop before the apex, so the RCA shares it, while a long LAD wraps around the apex onto the inferior wall. (Radiopaedia: Left anterior descending artery.)

The coronary veins generally run alongside the surface arteries. Most of their blood collects in the coronary sinus, a large, thin-walled vein on the back of the heart lying in the atrioventricular sulcus, which empties into the right atrium. (OpenStax Anatomy and Physiology 2e, 19.1: Heart Anatomy.)

The great cardiac vein is the largest tributary. It starts at the apex, climbs the anterior interventricular groove and widens into the coronary sinus. The middle cardiac vein (posterior interventricular vein) climbs the posterior groove from the apex. The small cardiac vein runs in the groove between the right atrium and right ventricle. The posterior cardiac vein drains the back of the left ventricle. (TeachMeAnatomy: Arterial Supply and Venous Drainage of the Heart.)

Radiopaedia lists the usual tributaries of the coronary sinus as the great, middle and small cardiac veins, the posterior vein of the left ventricle, the oblique vein of the left atrium (of Marshall) and the left marginal vein, and notes that the pattern varies a lot. The opening of the sinus into the right atrium is partly covered by the Thebesian valve. (Radiopaedia: Coronary sinus.)

Not all cardiac blood goes through the coronary sinus. The anterior cardiac veins drain the front of the right ventricle straight into the right atrium. (OpenStax Anatomy and Physiology 2e, 19.1: Heart Anatomy.)

The smallest cardiac veins (Thebesian veins, venae cordis minimae) drain the innermost, subendocardial layer of the myocardium directly into the chambers of the heart. They form the smaller cardiac venous system, alongside the larger system of veins on the outer surface. (Kenhub: Smallest cardiac veins (Thebesian veins).)

The coronary sinus matters in practice. It is the route for the left ventricular lead in biventricular pacing (cardiac resynchronisation therapy), and it can carry blood from a persistent left superior vena cava into the right atrium. (Radiopaedia: Coronary sinus.)

Coronary artery disease is the leading cause of death worldwide. Fatty plaque builds up in the artery wall and narrows the lumen, reducing blood flow (ischaemia, US ischemia) and oxygen delivery (hypoxia) to the heart muscle beyond it. (OpenStax Anatomy and Physiology 2e, 19.1: Heart Anatomy.)

Myocardial infarction (MI) is the formal term for a heart attack. It usually follows sudden blockage of a coronary artery, and the heart muscle cells in that artery's territory die. Anastomoses between the coronary arteries are small, so they rarely protect the muscle when a main branch closes suddenly. (OpenStax Anatomy and Physiology 2e, 19.1: Heart Anatomy.)

Because each artery feeds a predictable area, the ECG leads that show changes during an infarct point to the culprit artery: the inferior leads (II, III, aVF) to the RCA, V1 and V2 (anteroseptal) to the LAD, I, aVL, V5 and V6 (anterolateral) to the circumflex, and I, aVL and V2 to V6 (extensive anterior) to the proximal left coronary artery. (TeachMeAnatomy: Arterial Supply and Venous Drainage of the Heart.)

The coronary arteries are shown by coronary angiography: a catheter is inserted through the femoral artery and contrast dye is injected into the coronary arteries. A narrowing can be widened with a balloon (angioplasty), and a stent may be left to hold it open. (TeachMeAnatomy: Arterial Supply and Venous Drainage of the Heart.)

The 3D model on this page comes from BodyParts3D, an adult male data set. It shows the left and right coronary trunks, the LAD with its diagonal and septal branches, the circumflex, the right marginal branches, the posterior interventricular branch and the main cardiac veins, but it does not label dominance or every small branch.

Anterior cardiac vein

The anterior cardiac veins are small veins that drain the front of the right ventricle directly into the right atrium.

Circumflex branch of coronary artery

The circumflex artery is a main branch of the left coronary artery that runs around the left side of the heart.

Conus branch of anterior interventricular branch of coronary artery

This is a small branch of the left anterior descending artery that supplies the right ventricular outflow tract.

Coronary sinus

The coronary sinus is the main vein of the heart, draining most of the blood from the heart wall into the right atrium.

Diagonal branch of anterior descending branch of coronary artery

The diagonal branches arise from the left anterior descending artery and run over the anterolateral wall of the left ventricle.

First anterior branch of anterior interventricular branch of coronary artery

The first of the right ventricular (right anterior) branches of the left anterior descending artery.

First anterior ventricular branch of coronary artery

This is the first anterior ventricular branch of the right coronary artery.

First posterior ventricular branch of coronary artery

This is the first posterior ventricular branch of the right coronary artery.

First septal branch of posterior interventricular artery

This is the first septal perforating branch of the posterior interventricular artery.

Great cardiac vein

The great cardiac vein is the largest tributary of the coronary sinus and drains the front of the heart.

Marginal branch of coronary artery

A branch of the coronary artery running along the margin of the heart.

Marginal vein

The marginal veins of the heart, running along its right (acute) and left (obtuse) margins.

Middle cardiac vein

A coronary vein running in the posterior interventricular groove.

Posterior interventricular branch of coronary artery

The artery in the posterior interventricular groove supplying the back of the ventricles.

Posterior vein of ventricle

The posterior vein of the left ventricle, a tributary of the coronary sinus.

Second anterior branch of anterior interventricular branch of coronary artery

The second right ventricular (right anterior) branch of the left anterior descending artery.

Second septal branch of posterior interventricular artery

A septal branch of the posterior interventricular artery.

Septal branch of anterior interventricular artery

One of the septal branches of the left anterior descending artery.

Small cardiac vein

A coronary vein along the right margin of the heart.

Third anterior branch of anterior interventricular branch of coronary artery

The third right ventricular (right anterior) branch of the left anterior descending artery.

Trunk of anterior interventricular branch of coronary artery

The main stem of the left anterior descending artery.

Trunk of coronary artery

The main stems of the right and left coronary arteries, from their openings in the aortic sinuses to their first divisions.