Chambers and valves of the heart

The heart has 4 main sections, or "chambers." The top 2 chambers are called the right atrium and left atrium. The bottom 2 chambers are called the right and left ventricles. Each of these chambers has a valve that keeps blood flowing in 1 direction. The valves in this picture appear in gray.

When the heart is working normally, blood comes in from the body through the right atrium and into the right ventricle. From there, it goes to the lungs, where it picks up oxygen. Then, the blood comes back through the left atrium, into the left ventricle, and back out to the body through a blood vessel called the aorta. The aorta appears in red. If a valve doesn't work properly, it will either let blood flow backward in the wrong direction or not let enough blood flow forward.