Most heart attacks are caused by a clot that blocks one of the coronary arteries (the blood vessels that bring blood and oxygen to the heart muscle). The clot usually forms in a coronary artery that has been previously narrowed from changes related to atherosclerosis. The atherosclerotic plaque (buildup) inside the arterial wall sometimes cracks, and this triggers the formation of a thrombus, or clot.

A clot in the coronary artery interrupts the flow of blood and oxygen to the heart muscle, leading to the death of heart cells in that area. The damaged heart muscle permanently loses its ability to contract, and the remaining heart muscle needs to compensate for it.

Rarely, sudden overwhelming stress can trigger a heart attack.

It is difficult to estimate exactly how common heart attack is because many patients die before seeking medical help (perhaps as many as 200,000 to 300,000 in the United States per year). It is estimated that approximately 1 million patients visit the hospital each year with some type of MI as their principal diagnosis.

The risk factors for coronary artery disease and heart attack include:

• Smoking
• Hypertension (high blood pressure)
• High-fat diet
• High blood cholesterol (LDL) levels
• Diabetes
• Male gender
• Age
• Heredity

Newer risk factors for coronary artery disease have been identified over the past several years, including elevated homocysteine and C-reactive protein levels. Homocysteine levels can be treated with folic acid supplements in the diet. Studies are still ongoing about the practical value of these new factors.

Heart attack accounts for 1 out of every 5 deaths. It is a major cause of sudden death in adults.