Your heart is really a muscle. It's located a little to the left of the middle of your chest, and it's about the size of your fist. There are lots of muscles all over your body - in your arms, in your legs, in your back, even in your behind. But this muscle is special because of what it does - the heart sends blood around your body. The blood provides your body with the oxygen and nutrients it needs. It also carries away the waste that your body has to get rid of.

Your heart is sort of like a pump, or two pumps in one. The right side of your heart receives blood from the body and pumps it to the lungs. The left side of the heart does the exact opposite: it receives blood from the lungs and pumps it out to the body. By the time you're grown up, your heart will be beating (pumping) about 70 times a minute.

How does the heart beat? Before each beat, your heart fills with blood. Then it contracts to squirt the blood along. When something contracts, it squeezes tighter - try squeezing your hand into a fist. That's sort of like what your heart does so it can squirt out the blood. Your heart does this all day and all night, all the time. Every day, an adult heart pumps 2,000 gallons (7,500 liters) of recycled blood by filling and contracting. The heart is one tough worker!