The heart is the main organ in the circulatory system. It is on the left side of the human body and is about the size of a fist. The heart is divided into four chambers. They are the right and left atria and the right and left ventricles.

The heart is one of the most important organs in the human body because it is responsible for pumping the blood through out the entire body. The body needs the blood it contains oxygen to help the cells in the body function. The heart is an instrument that pumps the blood around the entire human body and is in the circulatory system. The heart pumps five liters of blood.

The heart pumps the blood around the body by way of the arteries, veins, and capillaries. Blood first comes to the heart through the superior and inferior vena cavas. Then the...