Heart attack occurs when blockage develops in the blood vessels that supply the heart muscle. Heart attacks are one of the most common causes of illness and are the leading cause of death in the United States. Certain conditions (“risk factors”) increase a person's chance of having a heart attack or other cardiovascular event. They include older age, male sex, high blood pressure, diabetes, smoking, high levels of total or low-density lipoprotein (“bad”) cholesterol or low levels of high-density lipoprotein (“good”) cholesterol in the blood, and close relatives who had heart attacks before 60 years of age. Aspirin decreases the chances of a heart attack in people who have had previous heart attacks (secondary prevention) and in people who have risk factors but have not yet had a heart attack (primary prevention). Statins are medications that treat high blood cholesterol levels. Many studies show that statins are effective in the primary and secondary prevention of heart attacks and other cardiovascular events. Although aspirin and statins are each known to be effective in the primary prevention of heart attacks and other cardiovascular events, the cost-effectiveness of using 1 drug, the other, or both drugs together is not known.