Before explaining what a heart valve leak is, let's talk about heart valves. There are four valves in the heart: mitral valve, aortic valve, tricuspid valve and pulmonary valve. The function of these valves is to ensure that blood flows in the right direction. For example, blood that is cleaned in the lungs and comes to the left atrium passes through the mitral valve and comes to the left ventricle. At this point, leakage in the mitral valve causes blood to be left behind.