Noninvasive techniques are particularly helpful in evaluating the function of mechanical prostheses and tissue valves. Combined phonocardiography with M-mode echocardiography, cinefluoroscopy, and Doppler echocardiography are the most useful noninvasive techniques in differentiating normal from abnormal metallic prosthetic valve function. The intensity of the opening and closing clicks and associated murmurs will depend on the type of prosthetic valve, the heart rate and rhythm, and the underlying hemodynamic status. Arrhythmias and/or conduction disturbances may produce motion patterns that mimic the echocardiographic signs of malfunctioning prosthetic valves. Two-dimensional echocardiography is of limited help in assessing patients with metallic prosthetic valves because of reverberating artifacts and side lobe echoes. However, 2-D echo is extremely useful in excluding underlying left ventricular dysfunction. In addition, 2-D echo allows the determination of the precise alignment of the prosthetic valves so that optimal M-mode evaluation of the disc or poppet motion can be undertaken. Two-dimensional echocardiography also allows diagnosis of pericardial effusion and exclusion of other valvular abnormalities. Differentiation of thrombus formation or tissue ingrowth from paravalvular regurgitation or dehiscence is possible by echophonocardiography, Doppler echocardiography, and cinefluoroscopy. Doppler echocardiography is the most sensitive noninvasive technique in diagnosing paravalvular leaks. In addition, significant obstruction across a prosthetic valve can be determined by calculation of maximal gradient across the obstructed orifice using Doppler echocardiography. The differentiation between "benign physiological regurgitation" from true "pathological regurgitation" by Doppler is not always possible. Disc variance is a potentially serious and lethal problem with the older Beall valves and can be detected readily by a combination of echophonocardiography, cinefluoroscopy, and Doppler echocardiography. With regard to bioprosthetic valves, 2-D echo is superior to M-mode in detecting primary valve failure. In addition, detection of vegetations, valve alignment, ring and individual leaflet motion can be readily accomplished by 2-D echo. When considering the value of noninvasive techniques in prosthetic valve function, it is essential to recognize that the patients must serve as their own control in the follow-up assessment.