Atherosclerosis is a disease of the arterial wall in which the layer thickens, causing narrowing of the channel and thus impairing blood flow. It can occur in any area of the body, but is most important when it happens in the heart, brain, or blood vessels leading to the brain.

The narrowing is due to the formation of plaques (raised patches) in the inner lining of the arteries. These plaques consist of low-density lipoproteins, decaying muscle cells, fibrous tissue, clumps of blood platelets, cholesterol, and sometimes calcium. They tend to form in regions of turbulent blood flow, and are found most often in people with high concentrations of cholesterol in the bloodstream.

The number and thickness of plaques increases with age, causing loss of the smooth lining of the blood vessels and encouraging the formation of thrombi (blood clots). Sometimes fragments of thrombi break off and form emboli, which travel through the bloodstream and block smaller vessels.

Atherosclerosis is responsible for more deaths in the U.S. than any other condition. Atherosclerotic heart disease, involving the coronary arteries (coronary heart disease), is the most common cause of death, accounting for one-third of all deaths. Atherosclerotic interference with blood supply to the brain (stroke) is the third most common cause of death after cancer.

Treatments for atherosclerosis are varied. Medication is unsatisfactory for treating atherosclerosis, since the damage has already been done. Anticoagulant drugs have been used to try to minimize secondary clotting and embolus formation. Vasodilator drugs are helpful in providing symptom relief, but are of no curative value. Surgical treatment is available for those unresponsive to medical treatment or in certain high-risk situations. Balloon angioplasty can open up narrowed vessels and promote an improved blood supply.

The blood supply to the heart can also be restored by coronary artery bypass surgery. Large atheromatous and calcified arterial obstruction can be removed by endartectomy, and entire segments of diseased peripheral vessels can be replaced by woven plastic tube grafts.