Atherosclerosis is a form of arteriosclerosis in which the inner layers of artery walls become thick and irregular because of deposits of fat, cholesterol and other substances. This buildup is called plaque and can cause arteries to narrow, reducing the blood flow through them. Eventually plaque can erode the wall of the artery and diminish its elasticity. Plaque deposits can rupture, causing blood clots to form at the rupture that can block blood flow or break off and travel to another part of the body. This is a common cause of heart attack or ischemic stroke.