The heart is made of muscle. It has four hollow chambers each separated by valves. The valves are responsible for allowing blood in and out of the heart.
The two top chambers are called atria. The chambers on the bottom are called ventricles.
The heart pumps out and receive blood through blood vessels. Arteries take blood containing oxygen and food and send it to the body.
Arteries grow smaller as they go further from the heart. They branch off into small blood vessels.
Veins take deoxygenated blood from the body and carry it to the heart.