The heart pumps blood to carry oxygen and nutrients to every organ and muscle in the body. The heart needs its own supply of blood, too.

The vessels that supply oxygen-rich blood to the heart are called coronary arteries. The coronary arteries are about the width of a drinking straw, approximately 1/8 inch (4 mm) wide and gradually taper as they descend on the heart.

There are two main coronary arteries – the left main coronary artery and the right coronary artery. The left main coronary artery divides into two branches called the left anterior descending (LAD) artery and the left circumflex artery. These larger arteries wrap around the outside of the heart and subdivide, like branches on a tree, into smaller and smaller "marginal" coronary arteries that run around the outside of the heart and send even smaller arteries inward.