In figure B, the heart is the muscle in the lower half of the picture. The heart has four chambers. The heart’s upper chambers, the right and left atria (AY-tree-uh), are shown in purple. The heart’s lower chambers, the right and left ventricles (VEN-trih-kuls), are shown in red.

Some of the main blood vessels (arteries and veins) that make up your circulatory system are directly connected to the heart.