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Heart Disease Health Center

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Heart Disease and Heart Attacks

More than 1 million Americans have heart attacks each year. A heart attack, or myocardial infarction (MI), is an event that causes permanent damage to the heart muscle. "Myo" means muscle, "cardial" refers to the heart and "infarction" means death of muscle tissue due to lack of blood and oxygen supply.

What Happens During a Heart Attack?

Heart muscle requires a constant supply of oxygen-rich blood to nourish it. The coronary arteries provide the heart with this critical blood supply. If you have coronary artery disease, those arteries become narrow -- or obstructed -- and blood cannot flow as well as it should. Fatty matter, calcium, proteins and inflammatory cells build up within the arteries to form plaques of different sizes and consistencies.

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The outer surface of the plaque may rupture or crack and platelets (disc-shaped particles in the blood that help form blood clots) then come to the area to form blood clots around the plaque -- like a scab. If a blood clot totally obstructs the artery, the heart muscle can become starved for oxygen. This is called ischemia. And within a short time (even minutes), death of heart muscle cells occurs, causing permanent damage. This is a heart attack.

While it is unusual, a heart attack can also be caused by a spasm of a coronary artery. Coronary arteries have a muscle lining which can contract or relax depending on the needs of the heart muscle at a given time. During a coronary spasm, the coronary arteries constrict or spasm without warning, reducing blood supply to the heart muscle and potentially causing a heart attack. It may occur at rest and can even occur in people without significant coronary artery disease.

Each coronary artery supplies blood to a specific region of heart muscle. The amount of damage to the heart muscle depends on the size of the area supplied by the blocked artery and the time between injury and treatment. Earlier treatment can reduce the impact of the heart attack.

Healing of the heart muscle begins soon after a heart attack and takes about eight weeks. Similar to a skin wound, the heart's wound heals and a scar will form in the damaged area. However, the new scar tissue does not contract. Therefore, the heart's pumping ability can be reduced after a heart attack. The amount of lost pumping ability depends on the size and location of the scar.

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