How does the heart work?
Your heart is made of muscle, and has two chambers, called the atrium and the ventricle, on each side. About 100 000 times a day, the heart fills with blood and then contracts to pump the blood out again. This contraction is called a heartbeat. Deoxygenated blood from your body flows into the right side of your body flows into the right side of your heart, and is pumped to the lungs, where it takes in oxygen. The oxygenated blood returns to the left side, which pumps the blood returns to the left side, which pumps the blood out through a large artery called the aorta and around your body. Each side of your heart has two valve. These are flaps that stop blood flowing backwards after each beat.