The newly oxygen-rich blood (shown in red) returns to the heart and enters the left atrium. Blood flows through the left atrium into the left ventricle. The left ventricle pumps the oxygen-rich ...

open as wide as it should, restricting blood flow through the heart - this means less blood reaches the body, pressure builds up and the lungs can swell with fluid close properly and allow blood ...

Originally appeared on the NOVA Web site Cut to the Heart. Let's get straight to the heart of the matter—the heart's job is to move blood. Day and night, the muscles of your heart contract and ...