Arteriosclerosis is the build-up of deposits called plaque in inner lying of an artery. Plaque is made of fatty substances, cholesterol, cellular waste products, calcium, and fibrin, which is a clotting material in the blood. The inner layer of the artery becomes thickened due to the buildup of the plaque. This reduces the amount of blood flow and oxygen supply to the surrounding muscle. If the oxygen supply to a portion of heart muscle is reduced or completely occluded, a heart attack can occur. If the oxygen supply to a portion of brain is cut off, a stroke can occur.