It occurs when fatty substances accumulate in the inner lining, or walls of an artery. A patch of this is called plaque.
Plaques can affect both large and medium sized arteries.
How plaques begin or what causes them isn't known. Over time, however, the lining of important blood vessels can become thick and hard. A heart attack occurs when the flow of blood through an artery that leads to the heart muscle becomes blocked by plaque. If the artery brings blood to a leg or arm and it becomes blocked, this can cause numbness, pain and gangrene may develop. When an artery in the brain becomes blocked, a stroke results.