The blood is the body's transport system. Its main function is to carry both fuel and the oxygen for burning the fuel to every living tissue. It also carries waste matter away from the tissues and helps maintain body temperature. To do all this, it must circulate continuously. Basically, the heart consists of two pumps side by side.
Blood is pumped from the right side to the lungs, where waste gases are removed and oxygen added.
Freshly oxygenated blood returns to the left side, from which it is pumped to all organs and tissues. Blood flows away from the heart, either to the lungs or the rest of the body, through arteries, which branch again and again, getting smaller. The smaller arteries are called arterioles. The arterioles go on branching, getting increasingly narrower until they become tiny capillaries. Only the most common of the many disorders of the heart and circulation are discussed in this section.