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Before each beat, your heart fills with blood. Then its muscle contracts to squirt the blood along. When the heart contracts, it squeezes. Your heart does this all day and all night. It never stops while you are alive. Your hearts never stops beating while your alive.
The heart is made up of four chambers: two atria and two ventricles. The right atrium receives oxygen-poor blood from the body and pumps it to the right ventricle. The right ventricle pumps the oxygen-poor blood to the lungs. The left atrium receives oxygen-rich blood from the lungs and pumps it to the left ventricle. The left ventricle pumps the oxygen-rich blood to the body.
Between the chambers there are valves which stop blood from flowing the wrong way. The valves open and close and help to move blood through the heart to the right place at the right time. When the valves open, blood surges into the chambers. The valves close, the heart contracts, and the blood flows out.
The blood moves through many blood vessels called arteries and veins. The blood vessels that carry blood away from the heart are called arteries. The ones that carry blood back to the heart are called veins. Blood delivers oxygen to all the body's cells. Without oxygen, these cells would die. Your arteries carry blood away from the heart.