The human heart is a little bigger than the fist and is located just behind the sternum or breast bone, a little to the left. The heart pumps blood to the various parts of the body and receives blood with carbon dioxide, which is pumped to the lungs for oxygenation.
The heart has four chambers; the right atrium, right ventricle, the left atrium and left ventricle.
Blood from the body and head enters the right atrium of the heart through a large vein, the vena cava. From here, blood passes to the right ventricle to the lungs where it loses the carbon dioxide and gets more oxygen. It then returns to the left atrium of the heart, from where it flows to the left ventricle and thereafter to the various parts of the body and brain. There is a bundle of nerves in the wall of the right atrium called the sinus node from which electrical impulses enable the pumping action of the heart.