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 the heart 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 waste.
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.
The heart is made up of four different blood-filled areas, and each of
these areas is called a chamber.
There are two chambers on each side of the heart. One chamber is on the top and
one chamber is on the bottom. The two chambers on top are called the atria. If you're talking only about
one, call it an atrium. The atria are the chambers that fill with the blood
returning to the heart from the body and lungs.
The two chambers on the bottom are called the ventricles. Their job is to squirt
out the blood to the body and lungs. Running down the middle of the heart is a
thick wall of muscle called the septum.
The septum's job is to separate the left side and the right side of the heart.
The atria and ventricles work as a team - the atria fill with blood,
then dump it into the ventricles. The ventricles then squeeze, pumping blood
out of the heart. While the ventricles are squeezing, the atria refill and get
ready for the next contraction.