The circulatory system transports food, oxygen, carbon dioxide, and waste throughout the body via blood flowing through blood vessels. Blood is pumped from the heart through arteries and returns to the heart via veins, with the smallest blood vessels being capillaries. The heart has four chambers that cycle blood receiving oxygen from the lungs and pumping it out to the entire body. Unhealthy eating and lack of exercise can increase risks of heart problems like heart attacks by clogging arteries.