Heart cross-section - image description

The illustration shows a cross-section of the heart. It shows the four different chambers of the heart: the right atrium, the left atrium, the right ventricle and the left ventricle. The atria are at the top and the ventricles at the bottom of the heart. Between the atrium and the ventricle on each side is a valve. There are also valves in the blood vessels going in and out of the heart. In the illustration, some valves are open and other valves are closed. The illustration has arrows to show the direction that the blood flows through the heart.