There are two types of valves:
Atrialventricular, which control the flow of blood from atria (small chambers of the heart) to ventricles (large chambers of the heart). These are the mitral valve (from the left atrium to the left ventricle) and the tricuspid valve (from the right atrium to the right ventrical)
There are several pathologies of the heart valves. Rarely, an infection will attack a valve, but when this happens, it is very difficult to treat. More often, a valve will harden. This allows blood to flow back through the valve - regurgitation. In such cases, the valve must be replaced, either with an artificial valve or one taken from an animal, usually a pig. Regurgitation can be auscultated in some cases.