Coronary Circulation

The left and right coronary arteries originate from the ascending aorta and supply oxygenated blood to the myocardium. These arteries encircle the heart in the coronary sulcus, forming a separate circulation system distinct from the systemic and pulmonary circulation. This coronary circulation is the shortest circulation in the body and nourishes the heart muscle itself.

The left coronary artery divides into two major branches: the left anterior descending artery (LAD) and the circumflex artery. The LAD follows the anterior interventricular sulcus and supplies blood to the anterior two-thirds of the interventricular septum and anterior walls of both ventricles. The circumflex artery supplies the left atrium and posterior walls of the left ventricle.

The right coronary artery divides into the right marginal artery and the posterior descending artery (PDA). The right marginal artery serves the lateral right side of the heart, while the PDA runs in the posterior interventricular sulcus to supply posterior ventricular walls. Together, these branches supply the right atrium and almost all of the right ventricle.

Anastomoses are connections that link different coronary arteries, providing alternate routes for blood supply when arteries become blocked. These interconnections ensure the myocardium receives adequate oxygenated blood even if one artery is compromised, serving as a critical safety mechanism for heart function and survival.

Deoxygenated blood is collected by cardiac veins that roughly follow the paths of coronary arteries. The great cardiac vein, middle cardiac vein, and small cardiac vein join to form the coronary sinus, an enlarged vessel that transports deoxygenated blood to the right atrium. Anterior cardiac veins also empty directly into the right atrium.

Coronary arteries deliver blood when the heart is relaxed but become less effective during ventricular contraction because the contracting myocardium compresses these vessels. This pulsating blood flow pattern reflects the heart's mechanical activity. Despite accounting for only 1/200 of body weight, the heart requires about 1/20 of total blood supply.

Heart dominance determines the origin of the posterior descending artery (PDA). In 70-80% of right-dominant individuals, the PDA stems from the right coronary artery. About 5-10% are left-dominant, with the PDA originating from the circumflex artery, while 10-20% have codominant circulation where both arteries supply the PDA.