The human heart has four chambers. The two upper chambers are called the atria. The two lower chambers are called the ventricles. The atria receive blood returning to the heart, and then push it downward to the ventricles. The ventricles, which are larger and stronger, give departing blood a push outward towards its destination.
Blood flows through the body in an endless, figure-eight loop.
The right ventricle pumps blood to the lungs so it can get oxygen. Blood returning from the lungs arrives in the left atrium, which pushes it downward to the left ventricle. Click Photo to Enlarge 3. The left ventricle pumps blood out to rest of the body, taking the oxygen out where it will be used by muscles and other tissues to do their work. Blood returning from various parts of the body arrives in the right atrium.