Coronary Circulation

The coronary circulation consists of the arteries and veins that supply and drain the myocardium (heart muscle). Unlike other tissues, the heart cannot extract oxygen efficiently from the blood within its chambers, so it requires a dedicated vascular system. Coronary circulation arises from the base of the ascending aorta and delivers oxygenated blood to the heart wall during diastole.

Coronary Arteries

The heart is supplied by two main coronary arteries:

• Right Coronary Artery (RCA)
• Left Coronary Artery (LCA)

These arteries arise from the right and left aortic sinuses, just superior to the aortic valve, and course along the surface of the heart within the epicardial fat, giving off multiple branches.

Right Coronary Artery (RCA)

• Origin: Right aortic sinus
• Course: Runs in the coronary sulcus between the right atrium and right ventricle

Main Branches:

• Right marginal artery: Supplies the right ventricular wall
• Posterior interventricular artery (PDA): Runs in the posterior interventricular sulcus; supplies the diaphragmatic surfaces of both ventricles and the posterior third of the interventricular septum
• SA nodal branch: Supplies the sinoatrial node in most individuals (60%)
• AV nodal branch: Arises near the crux of the heart and supplies the atrioventricular node

Left Coronary Artery (LCA)

• Origin: Left aortic sinus
• Course: Short main trunk (left main coronary artery) that quickly bifurcates into its two major branches

Main Branches:

• Left anterior descending artery (LAD): Also called anterior interventricular artery; travels down the anterior interventricular sulcus and supplies the anterior walls of both ventricles and the anterior two-thirds of the interventricular septum
• Circumflex artery: Curves around the left side in the coronary sulcus, giving off the left marginal artery and sometimes the posterior interventricular artery (in left-dominant circulation)

Coronary Artery Dominance

Dominance is determined by which artery gives rise to the posterior interventricular artery:

• Right dominant (≈70%): RCA gives rise to PDA
• Left dominant (≈10–15%): Circumflex branch of LCA gives rise to PDA
• Co-dominant (≈15–20%): Both RCA and LCA contribute to the posterior interventricular region

Coronary Veins

Venous blood from the myocardium is primarily drained by the coronary sinus and its tributaries, which empty into the right atrium.

Coronary Sinus

• Location: Posterior atrioventricular groove
• Drainage: Receives most of the venous return from the heart

Main Tributaries:

• Great cardiac vein: Accompanies the LAD; drains anterior left heart structures
• Middle cardiac vein: Accompanies the PDA; drains posterior interventricular region
• Small cardiac vein: Accompanies the right marginal artery; drains right heart structures
• Posterior vein of the left ventricle and oblique vein of the left atrium

Anterior Cardiac Veins

These veins drain directly into the right atrium from the anterior right ventricle without passing through the coronary sinus.

Thebesian Veins

Also called venae cordis minimae, these are tiny veins within the walls of all chambers that drain directly into the corresponding heart chambers. They are most numerous in the right atrium.

Blood Supply Summary by Region

Region	Primary Arterial Supply
Right atrium	RCA
Right ventricle	RCA and right marginal branch
Left atrium	Circumflex branch of LCA
Left ventricle	LAD and circumflex branches
Anterior 2/3 of interventricular septum	LAD
Posterior 1/3 of interventricular septum	PDA (RCA or LCA depending on dominance)

Topographic Summary

• Coronary arteries: RCA and LCA arising from aortic sinuses
• Major branches: LAD, circumflex, right marginal, posterior interventricular
• Drainage: Coronary sinus → right atrium
• Dominance: Defined by origin of the PDA