Like all the body's organs, the heart requires a constant supply of nutrients and oxygen to function normally. This is delivered through a specialised network of arteries called the coronary arteries.

The network consists of the right coronary artery (RCA) and the left main coronary artery (also known as the left main stem (LMS). The left main branches into the left anterior descending artery (LAD) and the circumflex (CX). These arteries and their branches wrap round the heart to supply the muscle with blood. Then the arteries are healthy they have a smooth lining that ensures unrestricted blood flow. When the heart requires extra blood (e.g. when you exercise), the arteries expand in diameter to allow greater flow of blood to the muscle.

As a result of long-standing lifestyle practices, the coronary arteries can become clogged with plaque – clusters of cells, fat, cholesterol and sometimes calcium- that accumulates along the lining of the arteries. This disease process, called atherosclerosis, causes the arteries to harden and narrow and the blood supply to the heart is reduced.

When the blood flow is insufficient, the heart muscle is starved of oxygen. This condition is called ischaemia. Ischaemia can produce angina (chest pain).

As plaque accumulates along the artery wall, a rupture or tear of the diseased lining of the artery can occur. This causes blood clots to form and further impede or abruptly interrupt blood flow. When this happens, the muscle of the heart is at risk of irreversible damage and the tissue can die. This is what happens in a heart attack (myocardial infarction). The extent of damage and the structures involved (muscle, electrical tissue, etc) determines whether the heart attack will be fatal

Sometimes a coronary artery can contract temporarily or go into spasm, disrupting blood flow to part of the muscle of the heart. Coronary artery spasm can occur in blood vessels that appear normal. However, it usually occurs in an artery that is already partly occluded with atherosclerosis. It is rare, but severe spasm can cause a heart attack.