How many chambers does a human heart have?

A human heart has four chambers: two upper atria and two lower ventricles.

The right atrium receives oxygen-poor blood returning from the body, and the right ventricle pumps it to the lungs. After picking up oxygen, blood enters the left atrium and then the left ventricle, which sends it through the aorta to the rest of the body. A muscular wall called the septum separates the right and left sides.

A common mix-up is confusing chambers with valves. The heart has four chambers and four main valves—the tricuspid, pulmonary, mitral, and aortic valves. Valves control one-way flow; they are not additional chambers. The atria mainly receive blood, while the ventricles provide the stronger pumping action.

This four-chamber arrangement supports double circulation: one loop carries blood between the heart and lungs, and another carries oxygen-rich blood between the heart and body. It keeps oxygen-poor and oxygen-rich blood largely separated, making oxygen delivery efficient.