The heart pumps blood to the body through a complex network of arteries. With exception of the coronary arteries, which nourish the heart itself, most arteries transport oxygen-rich blood away from the heart. Circulating in the blood are red blood cells, white blood cells, nutrients and other life-sustaining substances. Cholesterol and other fatty substances also circulate in the blood. Over time, these substances can be deposited in the artery walls, a condition called atherosclerosis. The deposited cholesterol, or plaque, can build up over time, causing hardening and narrowing of the otherwise smooth artery walls. When the walls of the artery become narrowed and hardened, blood flow is restricted. As the plaque accumulates, the buildup can become unstable and may break off or “rupture.” A condition called thrombosis, results when blood starts to coagulate, or clump together, at the site of the rupture, similar to the way blood clots to stop bleeding from a cut. The blockage, or thrombus, can grow larger, further restricting the flow of blood. The thrombus is also in danger of breaking from the site and traveling through the arteries. The blockage caused by a thrombus can be life threatening. A blockage in the coronary arteries may cause a heart attack while blockage in a cerebral artery may cause a stroke. Blockage in one of the major arteries of the body can prevent blood flow to an extremity or organ, causing pain and tissue damage to the area.