Doppler echocardiographic characteristics of 75 normally functioning Björk-Shiley mitral prostheses were studied in patients whose valvar function was considered normal by clinical and fluoroscopic evaluation. The mean Doppler peak and end-diastolic gradients were 9.01 +/- 3.23 mm Hg, and 2.36 +/- 1.0 mm Hg, respectively. The mean area of the mitral valve calculated by the half-time method was 2.58 +/- 0.38 cm2. No significant difference between the various Doppler parameters was found for the two different valve sizes (25 and 27 mm) studied. Trivial mitral regurgitation was detected in 21 (28%) cases. Doppler echocardiography was performed in six patients with suspected malfunction of the Björk-Shiley mitral prosthesis subsequently confirmed at operation. The end-diastolic gradients in the six patients were 16, 20, 10, 14, 16, and 24 mm Hg, respectively. The calculated areas of the mitral valve were 1.57, 1.37, 1.3, 1.5, 1.46, and 1.3 cm2, respectively. The values of the gradient and calculated areas in malfunctioning valves were very different from those found in normally functioning Björk-Shiley mitral prostheses. It is concluded that Doppler echocardiography is a very useful noninvasive technique for the study of the function of the Björk-Shiley mitral prosthesis and provides quantitative information regarding pressure gradients and valvar area.