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 relax to pump blood throughout your body. When blood returns ...

All blood vessels are specifically ... at high pressure as it leaves the heart; the largest artery is the aorta Contain valves to prevent back flow of blood Walls are made of semi-permeable ...

The semilunar valves stop the back flow of blood into the heart. There is a semilunar valve where the aorta leaves the left ventricle and another where the pulmonary artery leaves the right ventricle.