Nine young patients with normally functioning bi-leaflet mechanical prosthetic heart valves in the mitral or aortic positions were studied with digital phonocardiography and a signal processing technique known as digital deconvolution analysis. This analysis determines the temporal sequence of impacts produced by the valve's occluding element(s) striking the valve cage and characterizes the acoustic response to normal asynchronous impacting forces. Phonocardiographic signals were recorded with a high frequency accelerometer transducer and digitized at 8000 samples/s. Beat-to-beat variability in asynchrony of leaflet closure occurred with a difference of 0-9 msec between closure times of the two valve leaflets. Individual mean asynchrony values ranged from 1.9-5.8 msec, probably related to changing contours of initial reversing blood flow capturing each leaflet separately. Digital deconvolution analysis characterizes dynamic and structural properties of mechanical prosthetic heart valves and provides a simple noninvasive method for serial assessment of the valve's function.