Six different manufacturers' prosthetic heart valves were tested and ranked according to performance indices described by W. Swanson and S. Gabbay. Additionally, a technique was devised whereby the pressure drop across the aortic valve could be predicted by velocity measurements made with continuous wave Doppler (CWD) imaging. The results of preliminary in vitro studies demonstrate a high correlation (r>0.9) between the peak velocity as measured with CWD and the predicted velocity obtained by the application of a simplified Bernoulli equation, which uses a measured maximum pressure drop across the aortic valve. Also, an acoustical signature analysis technique is under investigation for possible non-invasive detection of partially-failed single leaflet type mechanical valves.