The Heart

The heart is a muscular pump the size of a man's fist which lies behind the sternum. It is hollow but divided into two separate chambers which are further divided into two smaller interconnecting chambers.

The top chambers are called atria and the bottom chambers are called ventricles.

The muscle contracts and the blood in each side is squeezed from the top into the bottom chamber, through a non return valve.

Blood from the right hand side goes to the lungs where it collects oxygen and flows back to the left side of the heart. From here it is pumped around the body and back to the right side of the heart and then to the lungs again. Blood always enters the heart via the upper chambers and leaves via the lower ones.

Go to Washington University web site where they have some excellent images of the heart. (Follow the link to the "Digital Anatomist Interactive Atlases" and browse through the images of thoracic organs that are listed at the bottom of the page.)