Transthoracic and transesophageal echocardiography were used to demonstrate prosthetic valve dysfunction in 134 patients with cardiac prosthetic valves in aortic, mitral and tricuspid position. Transthoracic echocardiography showed a high accuracy in the diagnosis of prosthetic valve dysfunction, especially in aortic position or when a stenosis was present. Transesophageal echocardiography allowed to verify the etiology and site of dysfunction and to show even minor leaks. Sixty-six patients underwent reoperation while 68 underwent a clinical and echocardiographic follow-up because only mild symptoms were present. Thus echocardiography represents the technique of choice in the follow-up of patients with prosthetic valves and it is able to help in decision making. However, cardiac catheterization is mandatory if a disagreement between clinical and echocardiographic data is present or when coronary artery disease is suspected or present.