How the Heart Works
The heart is a muscular, hollow organ that constantly pumps blood throughout the body. It is made up of strong muscle tissue, called heart muscle.
The heart has four chambers. The two upper chambers (atria) receive and collect blood. The two lower chambers (ventricles) pump blood.
The four heart chambers work together to contract and pump blood. As it circulates, blood delivers oxygen and nutrients throughout the body.
The Coronary Arteries
In order to keep pumping blood, the heart must have a continuous supply of oxygen. The coronary arteries are the vessels that carry oxygen-rich blood to the heart muscle.
As blood leaves the left ventricle, it is forced into the body's main artery, the aorta. At the very beginning of the aorta, near the top of the heart, emerge the two coronary arteries. They are referred to as the "left" and "right" coronary arteries.
The first segment of the left coronary artery is called the left main artery. It is about as wide as a drinking straw and less than an inch long.
The left main artery then branches into two slightly narrower arteries: the left anterior descending, which travels down the front side of the heart; and the left circumflex, which circles around the left side and then to the back of the heart.
The right coronary artery comes from the aorta, circles around the right side, and then to the back of the heart.
The coronary arteries travel on the surface of the heart and divide into smaller branches. They then penetrate deep into the heart muscle, carrying oxygen-rich blood to the cells.