How and why does the heart pump blood to itself?

Why doesn't the heart act like an opportunist and just take its oxygen straight from the blood that's constantly passing through its chambers? There are two important reasons. First, not all of the blood in the heart has oxygen. Remember, your heart is divided into four chambers: the left atrium and left ventricle, as well as the right atrium and right ventricle. The left side is receiving "good," oxygen-rich blood from your lungs, sending it through the left atrium down into the left ventricle, where the heart's contraction forces it through a valve into the aorta.

The left side of the heart would be OK if it took its oxygen right there in the chambers, but the right side would be out of luck. The right atrium handles "bad," oxygen-poor blood from all over the body and ships it down into the right ventricle. From there, the heart's contraction forces this bad blood out into the pulmonary artery, which forwards it to the lungs. This blood gains oxygen again, but it still returns to the side of the heart dealing in good blood -- the left side. The right side never sees oxygenated blood pass through it, so it needs its own supply.

The second reason for this tricky route is that the rest of the body wants fully oxygenated red blood cells, not just castoffs from the heart. If the heart replenished its own oxygen supply directly from the river of blood flowing through it, the blood leaving the heart would have less oxygen to deliver to the body. Instead, the muscle exercises some restraint and feeds itself through arteries that tap into the aorta, just like every other part of the body.

Once the aorta leaves the heart, blood can branch off almost immediately into the left coronary artery and the right coronary artery. The left artery splits into two large branches: the left anterior descending and the left circumflex.­Their names describe their routes along the surface of the heart -- circumflex just means the artery winds around the heart instead of hanging straight down. The right coronary artery supplies the right side of the heart, and branches off into the posterior descending artery. ­

­Interestingly, we don't all have the same network of arteries. Some people have a third main coronary artery that juts off the aorta, and others just have one main coronary artery. In addition, sometimes it's the right coronary artery, instead of the left, that branches into two more arteries.

Regardless of these differences, the result is the same: The arteries branch off into smaller arteries, and all the arteries and their branches wrap around the heart, like a crown (hence, the "coronary"). This way, all the heart's tissue receives a fresh blood supply, giving it the fuel it needs to pump day after day.

Next, we'll look at what happens when those coronary arteries don't deliver all the fuel that the heart needs. It's not good.

Your heart receives its blood from the coronary arteries. These arteries begin life big, soft and smooth inside. As we grow older, we damage those once-supple arteries with stress, fast food, not enough exercise and age. Over decades, they collect plaque (or fatty deposits) along their inner walls, causing them to harden and narrow. This condition is known as atherosclerosis. Unchecked, atherosclerosis may worsen and become coronary artery disease (also known as coronary heart disease). Doctors tend to shorten it to just CAD or CHD.

As CAD advances, a number of things can happen. For example, if a portion of your heart muscle is receiving some -- but not enough -- oxygen due to partially blocked arteries, it won't be permanently damaged, but the muscle won't like the situation one bit. It files a formal complaint with you in the form of chest pain called angina. Stable angina is the lesser of two evils; it's predictable and reversible. Unstable angina, however, could signal an unstable plaque that could cause a heart attack.

You may not feel this chest pain when you're relaxing because your heart doesn't require much blood when you're sunning yourself by the pool. If you start swimming laps, however, it needs more than your narrowed arteries can deliver, and this hurts.

Blockages lower the amount of oxygen getting to the heart muscle. If one of these obstacles breaks open, a clot forms at the site of the rupture in the plaque. This little clot can totally block the artery within minutes. When heart tissue is cut off from oxygen, it quickly begins to die. This, typically, is your heart attack (or myocardial infarction).

If your coronary arteries become dangerously blocked, doctors may discuss one of the following procedures with you.

Angioplasty: This procedure uses a tiny balloon to open a clogged artery. A balloon catheter is inserted into an incision near the groin and threaded up through an artery into the heart. Then doctors inject dye and search for blockages. Once found, they put the catheter through the blockage narrowing and inflate the balloon. This procedure won't stop the arteries from hardening again, but it will lessen the pain and other symptoms of CAD by increasing the blood flow.

Stenting: Sometimes, in addition to or instead of angioplasty, a metal or plastic tube called a stent may be inserted into a blocked artery to prop it open. Doctors may perform angioplasty and stenting on a patient before, after or during a heart attack. Some cardiologists prefer just stenting without angioplasty. The drawback of this procedure is that stents can clog, just like your arteries.

Coronary artery bypass graft (CABG): During a "traditional" CABG, your heart is stopped, and you're placed on artificial respiration. A vein or artery that won't be missed too much is taken from somewhere else, possibly your arm or leg. Surgeons attach one end of the graft to the aorta and the other end to the troubled artery on the far side of the blockage. This detour enables blood to bypass the blockage and flow unobstructed from the aorta to the heart. Most grafts continue working properly for 10 or 15 years [source: Medline Plus]. When you hear the terms double-, triple- or even quadruple-bypass surgery, it refers to the number of arteries receiving bypass grafts.

The main thing your heart needs is the same thing it distributes to the rest of your body: oxygen-rich blood. By living a heart-healthy lifestyle, your heart should get the natural resources it needs to do what it does best, without the help of balloons, tubes or relocated veins or arteries. See the next page for lots more information about the heart.