Diagram of a Simplified Form of a Circulatory System

The vena cava brings into the heart deoxygenated blood from all parts of the body. This deoxygenated blood enters the right atrium, the blood moves into the right ventricle through the tricuspid valve and later pumped into the lungs through the pulmonary artery. The deoxygenated blood in the lungs becomes oxygenated because of the atmospheric oxygen taken into the lungs during breathing. The atmospheric oxygen in the lungs oxygentaes the deoxygenated blood that moves into the lungs from the right ventricle.

Now, the oxygenated blood returns to the heart through the pulmonary vein into the left atrium. It then moves into the left ventricle through the bicuspid valve.

The oxygenated blood is pumped from the left ventricle to the aorta and to all body parts. The sequence of the blood flow through the heart to the body part is shown.