Heart attack (“myocardial infarction”) 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. They include older age, male sex, high blood pressure, diabetes, smoking, high total or LDL (“bad”) cholesterol levels, low HDL (“good”) cholesterol levels, and close relatives with heart attacks before age 60. Aspirin decreases the chances of a heart attack in people who have had previous heart attacks or strokes, but its usefulness in people without such a history is unclear. Aspirin can have uncommon but serious complications, such as bleeding in the digestive tract or in the brain.