The four chambers of the heart are the right atrium, left atrium, right ventricle and left ventricle. The atria are the two upper chambers that receive blood from the veins. The ventricles are the two lower chambers that pump blood into the arteries.
The heart can be described as two separate pumps, a left pump and a right pump. The right atrium receives oxygen-poor blood. It channels this blood to the right ventricle, which pumps it to the lungs for oxygenation. The left atrium receives oxygen-rich blood from the lungs and transfers it to the left ventricle for distribution to the body.