Flexi Says: Your heart pumps blood through a network of blood vessels. The network and your heart together are called a “circulatory” system. It's called a circulatory system because the blood circulates around and around. You also know that your blood carries oxygen to all of the cells in your body. The blood gets the oxygen from your lungs, which is a part of your breathing machine called the respiratory system. What you might not know is that your heart is really two pumps in one. It pumps the blood through two connected circuits. One circuit goes to the lungs, and one circuit goes to the rest of the body. So a map of the circulatory system is really more like a figure eight than a circle.