Your heart is a hollow, muscular organ whose only job is to pump blood throughout your body. Because every cell in your body must have a never-ending supply of oxygenated blood, your heart never sleeps. It beats about 100,000 times a day, pumping 6 qts of blood through the 65,000 miles of vessels that comprise your circulatory system, 3 times every minute.

Like every other organ in your body, your heart must have its own blood supply. Blood flows through your heart's four chambers, the right atrium and ventricle, which pump oxygen-depleted blood to the lungs, and the left atrium and ventricle, which pump newly oxygenated blood to the body. But the blood flowing through its chambers doesn't nourish the heart itself. That job is given to the coronary arteries, which wrap around the heart like a crown (hence the name "coronary," from the Latin word for crown). There are two main coronary arteries which branch out of the aorta, the left main coronary artery and the right coronary artery. These large coronary arteries are about the width of a drinking straw and gradually taper as they descend on the heart. The left main coronary artery divides into two branches called the left anterior descending artery and the circumflex artery. The right coronary artery branches into the posterior descending artery and the marginal artery. These arteries branch into smaller and smaller arteries, some of which penetrate inside the heart.

Because your heart works so hard, it requires a constant, uninterrupted flow of blood through the coronary arteries, and if that flow is impeded in any way, the results can be devastating.

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