Coronary circulation is the circulation of blood in the blood vessels that supply blood to and from the heart muscle. Although blood fills the chambers of the heart, the muscle tissue of the heart, or myocardium, is so thick that it requires coronary blood vessels to deliver blood deep into it. The vessels that deliver oxygen-rich blood to the myocardium are known as coronary arteries. The vessels that remove the deoxygenated blood from the heart muscle are known as coronary veins.

The coronary arteries that run on the surface of the heart are 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. These relatively narrow vessels are commonly affected by atherosclerosis and can become blocked, causing angina or a heart attack. (See also: circulatory system.) The coronary arteries that run deep within the myocardium are referred to as subendocardial.

The coronary arteries are classified as "end circulation", since they represent the only source of blood supply to the myocardium: there is very little redundant blood supply, which is why blockage of these vessels can be so critical.

Coronary anatomy

In general there are two main coronary arteries, the left and right.

• Right coronary artery
• Left coronary artery

Both of these arteries originate from the beginning (root) of the aorta, immediately above the aortic valve. As discussed below, the left coronary artery originates from the left aortic sinus, while the right coronary artery originates from the right aortic sinus.

Variations

Four percent of people have a third, the posterior coronary artery. In rare cases, a person will have one coronary artery that runs around the root of the aorta.

Occasionally, a coronary artery will exist as a double structure (i. e. there are two arteries, parallel to each other, where ordinarily there would be one).

Coronary artery dominance

The artery that supplies the posterior descending artery (PDA) and the posterolateral artery (PLA) determines the coronary dominance.

• If the right coronary artery (RCA) supplies both these arteries, the circulation can be classified as "right-dominant".
• If the circumflex artery (CX), a branch of the left artery, supplies both these arteries, the circulation can be classified as "left-dominant".
• If the RCA supplies the PDA and the CX supplies the PLA, the circulation is known as "co-dominant".