The coronary arteries run on the surface of the heart and are therefore called epicardial coronary arteries. These arteries, when healthy, are capable of autoregulation to maintain coronary blood flow at levels appropriate to the needs of the heart muscle (myocardium).
The exact anatomy of the myocardial blood supply varies considerably from person to person. A full evaluation of the coronary arteries requires cardiac catheterization.
In general there are two main coronary arteries, the Left and Right.
The left coronary artery (LCA) arises from the aorta in the left cusp of the aortic valve as the Left Main (LM) artery and eventually divides into two major arteries: the Left Anterior Descending (LAD), from which various Diagonal (D) and Septal (S) branches arise; and the Circumflex (Cx) Artery, from which Obtuse Marginal (OM) branches arise.
The right coronary artery (RCA) arises from the aorta in the right cusp of the aortic valve, and divides into a major branch, the Posterior Descending (PD) artery, and several smaller branches, including the Conus Branch (CB), the Sinus Node branch (SN), the Acute Marginal (AcM), and the Posterolateral left ventricular (PL) artery.
Depending on which artery supplies the greater portion of the myocardium, a person's coronary circulation can be classifed as "right-dominant" or "left-dominant".
The coronary arteries are classified as "end circulation", since they represent the only source of blood supply to the myocardium: there is no redundant blood supply, which is why blockage of these vessels can be so critical.