Atherosclerosis is a slow progressive disease in which cholesterol deposits form within the wall of blood vessels. Atherosclerosis begins with damage to the inner lining of blood vessels. Such injury commonly occurs with high blood pressure and smoking. The tissue behind the inner lining is exposed, which makes blood platelets sticky and causes smooth muscle cells to grow and fill in the area of injury. A partial blockage of the artery begins to form. Cholesterol particles become part of the growing deposit and cause further blockage of the blood vessel. Cholesterol deposits can be crumbly and may break apart, which causes a clot to form, suddenly blocking the artery. Or, deposits may grow slowly over time, causing gradually worsening blockage. Cholesterol deposits may also break off and block arteries elsewhere in the body, or weaken arteries causing vessel walls to balloon out (aneurysm).
Atherosclerosis can affect any artery of the body. When the arteries that supply blood to the heart muscle are blocked, a heart attack occurs. When brain arteries are blocked, this causes a stroke. Blockage in arteries in the legs can lead to gangrene, and blockage of arteries to the kidneys leads to kidney failure. Atherosclerosis in the aorta, the main artery coming from the heart, can cause the aorta to balloon (aortic aneurysm) and eventually rupture.