1. Oxygen-poor blood (shown in blue) flows from the body into the right atrium.
2. Blood flows through the right atrium into the right ventricle.
3. The right ventricle pumps the blood to the lungs, where the blood releases waste gases and picks up oxygen.
4. The newly oxygen-rich blood (shown in red) returns to the heart and enters the left atrium.
5. Blood flows through the left atrium into the left ventricle.
6. The left ventricle pumps the oxygen-rich blood to all parts of the body.