This is located between your lungs. Its function is to pump oxygen-rich blood throughout your body and oxygen-poor blood to your lungs, it is part of your cardiovascular system.

Cardiac muscle

Your heart is a powerful organ. It works constantly without ever pausing to rest. It is made of cardiac muscle, which only exists in the heart. Unlike other types of muscle, cardiac muscle never gets tired.

Four chambers

Your heart is divided into four chambers. The upper two chambers are called atria. They are joined to two lower chambers called ventricles. These are the pumps of your heart. One-way valves between the chambers keep blood flowing through your heart in the right direction. As blood flows through a valve from one chamber into another the valve closes, preventing blood flowing backwards. As the valves snap shut, they make a thumping, 'heart beat' noise.

Double pump

Blood carries oxygen and other substances around your body. Oxygen from your blood reacts with sugar in your cells to make energy. The waste product of this process, carbon dioxide, is carried away from your cells in your blood.
Your heart is a single organ, but it acts as a double pump. The first pump carries oxygen-poor blood to your lungs, where it unloads carbon dioxide and picks up oxygen. It then delivers oxygen-rich blood back to your heart. The second pump delivers oxygen-rich blood to every part of your body. Blood needing more oxygen is sent back to the heart to begin the cycle again. In one day your heart transports all your blood around your body about 1000 times.
Your right ventricle pumps blood to your lungs and your left ventricle pumps blood all around your body. The muscular walls of the left ventricle are thicker than those of the right ventricle, making it a much more powerful pump. For this reason, it is easiest to feel your heart beating on the left side of your chest.

Oxygen supply to your heart