Coronary artery disease (CAD) is the result of blockages in the heart's blood vessels. Low blood flow to the heart due to blocked vessels causes chest pain or “angina.” If angina lasts long enough, a section of heart muscle dies, a condition called myocardial infarction (or “heart attack”). Risk factors for CAD include older age, male sex, high blood pressure, diabetes, smoking, high levels of total or low-density lipoprotein (“bad”) cholesterol and low levels of high-density lipoprotein (“good”) cholesterol, and family history of CAD. Modifying these risk factors after a heart attack can reduce a person's chance of having another heart attack. Doctors advise patients who have had a heart attack to participate in organized programs, called cardiac rehabilitation programs or secondary cardiac prevention programs, to reduce cardiac risk. The programs provide education and counseling to help patients improve or eliminate factors that are associated with CAD (unfavorable cholesterol levels, high blood pressure, smoking, and physical inactivity). They also often, but not always, include supervised exercise. Previous studies have established that cardiac rehabilitation programs that include supervised exercise improve survival after heart attack. However, the effectiveness of cardiac rehabilitation programs that do not include supervised exercise is less clear.