We retrospectively evaluated the clinical and echocardiographic findings of 50 patients with documented malfunctioning of cardiac prosthetic valves. The prostheses, mechanical or biological, were in 24 cases in a mitral and in 26 cases in an aortic position. Prosthetic dysfunction was due to thrombosis, fibro-calcific degeneration, fibrous cloth, bacterial infection, dehiscence, mismatch. The clinical features were represented by cardiac insufficiency of different degrees, up to global congestive failure unresponsive to medical treatment, by sudden low-output syndrome, arrhythmias, angina. The changes in auscultatory findings have appeared important clues to prosthetic malfunction, but we stress the necessity of an instrumental documentation of the type and grade of dysfunction. Echocardiography has represented an essential tool for a rapid and accurate noninvasive diagnosis of prosthetic pathology. The echocardiographic examination, except 2 false negatives, has consistently provided informations useful for therapeutic decisions. In 7 cases in critical clinical conditions (refractory heart failure or shock) the echocardiographic examination has afforded the exact documentation and identification of prosthetic pathology, allowing by itself a surgical decision.