The body requires a constant source of oxygen-rich blood in order to function properly. Once the organs and tissues use up the oxygen, the blood flows to the heart to pick up more. It arrives in the chambers on the right side, after which it is pumped to the lungs. The lungs replenish the blood with oxygen, and send it back to the heart (this time, the left side). From there, it is pumped back out to the body.
