The most common form of heart disease is Atherosclerosis, also known as coronary heart disease or hardening of the arteries. It involves deposits of fatty substances, cholesterol, cellular waste products, calcium and fibrin (a clotting material in the blood) in the inner lining of an artery. The build-up that results, called plaque, may partially or totally block the blood's flow through the artery. This can lead to bleeding (hemorrhage) into the plaque or formation of a blood clot (thrombus) on the plaque's surface. If either of these occurs and blocks the entire artery, a heart attack or stroke (brain attack) may result.

Atherosclerosis affects large and medium-sized arteries. The type of artery and where the plaque develops varies with each person. Atherosclerosis is a slow, progressive disease that may start in childhood. In some people, this disease progresses rapidly in their third decade--in others it doesn't become threatening until they're in their fifties or sixties.

Exactly how Atherosclerosis begins or what causes it isn't known, but some theories have been proposed. Many scientists think Atherosclerosis begins because the innermost layer of the artery, called the endothelium, becomes damaged. Possible causes of damage to the arterial wall are elevated levels of cholesterol and triglyceride in the blood, high blood pressure and  cigarette smoke.

See American Heart Association for more information on Atherosclerosis (Coronary Artery Disease).