The application of Doppler echocardiography to the study of valvular function has recently been extended to include prosthetic valves. We have used Doppler echocardiography to evaluate 40 patients with porcine mitral valves (PMV) implanted 0.5 to 99 months prior to examination. Three parameters of PMV flow were assessed: maximum diastolic left ventricular inflow velocity (Vmax), pressure half-time (P1/2t), and presence or absence of mitral regurgitation (MR). Normally functioning PMV (n = 29) were characterized by Vmax less than or equal to 180 cm/sec and P1/2t less than or equal to 160 msec. Within this group, P1/2t was not correlated significantly with the age of the patient nor with prosthesis size. Doppler correctly identified all 10 patients with MR. Among these 10 patients, Vmax was 206 +/- 53 cm/sec, significantly higher than the mean observed in normally functioning prostheses (136 +/- 24 cm/sec, p less than 0.001). In eight patients with stenosis of the PMV, mean P1/2t was 220 +/- 63 msec, and in seven of eight, it was greater than or equal to 180 msec (p less than 0.001 compared to normals). We conclude that: (1) Vmax less than or equal to 180 cm/sec, P1/2t less than or equal to 160 msec, and absence of systolic turbulence in the left atrium characterize normally functioning PMV; (2) P1/2t greater than or equal to 180 msec identifies patients with stenosis of the PMV; and (3) Doppler echocardiography can detect MR and separate mitral from tricuspid regurgitation.