What do my heart and blood vessels do?

Your heart and blood vessels make up your circulatory (SIR-kyoo-la-TOR-ee) system. Your heart is a big muscle that pumps blood through your body. Your heart pumps blood carrying oxygen to large blood vessels, called arteries (AR-ter-eez), and small blood vessels, called capillaries (KAP-ih-lair-eez). Other blood vessels, called veins, carry blood back to the heart.