Your heart is the organ which pumps the oxygen-filled blood to all parts of your body. Your heart, which is about the size of your fist, has a wall which consists mostly of muscle. The contraction of the muscle in combination with the opening and closing of the valves results in the flow of blood around the body.

Like any muscle, your heart requires oxygen to work. Oxygen-rich blood is fed to the heart via the coronary arteries, which branch off from the aorta. These vessels lie on the surface of the heart and distribute blood to all areas of the heart muscle through a complex network of small vessels.

Coronary artery disease causes the blood supply to the heart muscle to become restricted by a coronary artery blockage called a stenosis. The stenosis is caused by a build up of fatty plaque or cholesterol, which is deposited inside the vessel wall. The stenosis results in insufficient flow of blood to the heart muscle, and results in a lack of oxygen.
If the build up of plaque is only mild you may not experience any noticeable symptoms at rest, and possibly only mild chest pressure or pain during exercise. However, if the blockage is more severe the disease leads to insufficient blood supply of the heart muscle which may result in chest pain (angina.), heart attack (myocardial infarction), or rhythm disturbances (arrhythmia). A heart attack results from a completely blocked vessel and may damage the heart muscle.