What is a heart attack?

Various factors may cause a cholesterol plaque in the coronary artery to become unstable and rupture into the channel of the artery, exposing the fatty contents of the plaque to the circulating blood. When blood comes in contact with this fatty material, rapid clotting of the blood occurs. If the blood clot is large enough, it can completely occlude the channel of the coronary artery and prevent any blood from supplying the portion of heart muscle supplied by that particular artery. Since heart muscle cells can survive only minutes to hours without oxygen, occlusion of the coronary artery results in death of part of the heart muscle--a heart attack. It is important to understand that the likelihood that a cholesterol plaque will rupture does not depend on the degree of narrowing that plaque causes. A plaque forming a 20% narrowing, 50% narrowing, or 90% narrowing are all capable of rupturing and causing a heart attack. This explains how a "minor" plaque which does not cause any symptoms can cause a heart attack without warning.