Heart valve diseases occur when one or more of the heart’s valves do not function properly, disrupting normal blood flow through the heart. The heart has four valves—mitral, aortic, tricuspid, and pulmonary—that open and close to ensure blood flows in the right direction. Valve diseases can include stenosis (narrowing of the valve), regurgitation (leakage of blood backwards through the valve), and atresia (a valve that does not form properly). These conditions can lead to serious complications, including heart failure and arrhythmias.