The heart of the matter.

Q: What sets off a heart attack?

A: In a myocardial infarction, one of the arteries that supply blood to the heart muscle--or myocardium --gets blocked. These aren't major blood vessels, like the aorta, which pump blood out of the heart. They are smaller ones that carry oxygen-rich blood to feed the heart muscle. If the plaque completely cuts off the flow of blood--or more often, if a blood clot gets stuck in an already-narrowed artery--the lack of oxygen damages, and eventually kills, the heart muscle.

Q: How can you tell if your arteries are clogging up?

A: Most people can't. Often the first sign of trouble is a heart attack. Some people have warning signs like angina pectoris--chest pain caused by too little oxygen reaching the heart. It usually occurs during exertion or even emotional excitement. More dangerous is unstable angina, which can vary in intensity and duration, and which can occur during rest. But most people have no symptoms until more than three-quarters of their coronary arteries are blocked off.

Q: Who gets heart attacks?

A: Your risk depends on several factors, some of which you can control and some of which you can't. You can't change being male (though after age 65 a woman's risk is almost as high), having a family history of heart disease before age 55, and growing older (four out of five heart disease deaths occur in people over 65).

The three most powerful risk factors you can change are:

* Smoking: Smokers have more than twice the risk of a heart attack. Fortunately, the risk drops rapidly when people quit.

* High Blood Pressure (at least 140 over 90): It adds to the heart's workload, and also increases the risk of stroke, kidney failure, and congestive heart failure (that's when the heart loses its ability to pump out all the blood that enters it).

* High Blood Cholesterol: Once it hits 240, your risk doubles. Also risky is "bad" LDL (low-density lipoprotein) cholesterol over 130 and "good" HDL (high-density lipoprotein) cholesterol below 35 (below 40 for women, says the American Heart Association).

Q: Does exercise have to be vigorous?

A: Not necessarily. If you haven't been exercising regularly, a brisk walk (at least three days a week for at least 20 minutes) can improve your cholesterol, triglycerides, and blood pressure.

To raise your HDL significantly, you've got to walk or jog at least 12 miles a week.

Q: How can diet reduce the risk of heart disease?

A: Most diet advice is designed to lower your LDL cholesterol. And you get the biggest bang for your buck by cutting back on saturated fats.

That means red meats, especially ground beef and fatty processed meats like sausage and hot dogs. It also means full-fat dairy products like whole milk, regular cheese, ice cream, and butter.

But don't ignore the substantial amounts of saturated fat in lower-fat foods like 2 percent milk, some "light" cheese, chicken (especially thighs and wings), and ground turkey with skin.

Q: Do hydrogenated oils raise cholesterol?

A: The trans fats that are formed when oils are hydrogenated (hardened) do appear to raise blood cholesterol levels, though not as much as saturated fats do. The problem is that trans fats don't have to be listed separately on food labels, so you can't tell how much a food contains. Until labels are clearer, stick to tub margarine (they have fewer trans fats than stick margarine), and avoid processed or deep-fat fried foods (like french fries, fried chicken, pies, doughnuts, and cakes) that contain partially hydrogenated oils.

Q: Can fiber lower cholesterol?

A: Foods rich in soluble fiber appear to, at least slightly. Good sources are oat bran, beans (other than green beans), oranges, and baked potatoes with skin. Wheat bran is rich in insoluble fiber, which doesn't lower cholesterol (although it's great at relieving constipation).

Q: What diet offers the best protection?

A: One with the least saturated fat (less than 7 percent of calories) and cholesterol (200 milligrams or less per day), with low levels of sodium (1,800 milligrams or less per day), and with plenty of foods rich in soluble fiber.

That means a largely vegetarian diet loaded with beans, grains, fruits, and vegetables.

Q: How long does it take for diet to lower cholesterol?

A: Four to six weeks. Quick, huh?