The heart muscle needs oxygen-rich blood to do its job. The vessels that feed the heart are called coronary arteries (shown in the diagram right) and they branch off from the body’s main artery, the ...

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.