 Welcome to the anatomy of the heart. Your heart is located in the center of your chest. It's muscular walls contract, which creates your heart beat and pumps blood throughout your body. As your blood moves around, it delivers oxygen and nutrients to every cell. A normal, healthy adult heart is about the same size as a clenched fist. Every heart has four chambers. These are the right atrium, the right ventricle, the left atrium, and the left ventricle. The two upper chambers, or atria, receive blood. The two lower chambers, or ventricles, pump blood. Blood returning from your body's organs and tissues enters the right atrium. Because this blood has provided oxygen to your body, it's very oxygen-poor. It moves to the right ventricle and out to the lungs to pick up more oxygen in a process called gas exchange. The now oxygen-rich blood travels into the left atrium and into the left ventricle before your heart pumps it to the rest of the body. Each chamber is separated by the cardiac muscle and valves. The valves effectively move blood throughout the heart by opening in only one direction. This forces the blood to pass through the chambers, into the lungs, and into your body without backing up or flowing backward. Watch as the valves open and close between the atria and ventricles. The atrioventricular, or AV, valves are between the atria and the ventricles on each side of the heart. They are the tricuspid and the bicuspid, or mitral, valve. The tricuspid is on the right side, and the bicuspid, or mitral, is on the left side. There are also two semi-lunar valves, the pulmonary and the aortic. The pulmonary is between the right ventricle and the pulmonary trunk, and the aortic is between the left ventricle and the aorta. When the AV valves close, they prevent blood from flowing back into the atria while the ventricles are contracting. The tricuspid has three flexible cusps, or flaps, and the bicuspid has two. Corda tendinii are attached to the papillary muscles, which are located in the ventricles. When these muscles contract, the white, string-like corda tendinii become taut. It is these corda tendinii together with the papillary muscles that keep the valves shut when the ventricle contracts. Finally, let's see how all of these muscles, chambers, and valves work together. Watch how blood flows through the heart. This diagram shows the blood entering the heart from the body. At this stage, it's oxygen-poor. After traveling to the lungs, it returns to the heart, oxygen-rich. The blood leaving the left ventricle is heading for the body. This process repeats itself over and over again to effectively deliver oxygen and nutrients to your body. Congratulations! You've completed the anatomy of the heart.