There are more than 50 types of heart disease, including infections, arrhythmias, and congenital heart defects, but there are three in particular that afflict a larger segment of the population. According to the American Heart Association's (AHA) Heart Disease and Stroke Statistics 2009 Update, of the estimated 80 million people who have heart disease, 73.6 million suffer from hypertension; 16.8 million, coronary heart disease; and 6.5 million, stroke. Here's a primer on the top three:

•High blood pressure: Called the "silent killer" because people are often unaware that they suffer from the condition, hypertension affects about one in three Americans. Unfortunately, when left untreated, the stress that high blood pressure places on the cardiovascular system can lead to heart attack or stroke. The best thing you can do is to keep regular tabs on your blood pressure, especially if you have a family history of hypertension, suffer from diabetes or other conditions that could compromise the health of your blood vessels, and engage or have engaged in a bad habit that can raise your blood pressure like smoking, heavy drinking, or overeating and making poor food choices.

•Coronary heart disease (CHD): Also known as coronary artery disease, CHD occurs when the blood vessels that supply the heart with oxygen-rich blood become comprised, often due to a condition called atherosclerosis in which lesions called plaque collect along the blood vessel walls. As these lesions grow, they lessen the flow of blood to the heart muscle, which often results in chest pain, or angina. If one of the lesions erupts, a blood clot forms, completely cutting off the heart from its supply of blood and oxygen. After a few minutes, the heart muscle begins to die, and without immediate medical treatment, the person suffering the attack will die too. The AHA says that of the 16.8 million Americans who suffer from CHD, having a heart attack is their first indication that they have the disease.

•Stroke: About 700,000 Americans are stricken by a stroke each year. There are three types: When plaque ruptures and a blood clot forms and blocks the blood supply to the brain instead of the heart, an ischemic stroke occurs; hemorrhagic strokes are triggered by blood vessels that burst and bleed into the brain; and transient ischemic attacks (TIAs), or mini-strokes, happen when the blood supply is temporarily obstructed. If you experience sudden numbness, confusion, dizziness, vision loss, and/or a severe headache, you should seek medical attention immediately. Depending on how soon a stroke is treated, its degree of severity, and which side of the brain is affected, the aftereffects of a stroke range from behavioral changes, speech loss, and vision problems to amnesia and paralysis.