Prosthetic shadowing of the left atrium may prevent detection of mitral regurgitation during transthoracic echocardiography. In 60 patients with mitral valves, Carpentier-Edwards (n = 20), St. Jude (n = 22), and cage-ball (n = 18), we blindly evaluated the accuracy of three transthoracic Doppler signs of significant (> 2+) mitral regurgitation: (1) color Doppler flow convergence, (2) a color Doppler jet of significant regurgitation in the left atrium, and (3) an intense continuous wave Doppler signal. All 60 patients had transesophageal echocardiography, 26 had cardiac catheterization, and 28 had surgery. The sensitivity and specificity of flow convergence for significant regurgitation by transesophageal echocardiography was 73% and 70%, respectively, compared with 33% and 93% for left atrial color Doppler, and 15% and 97% for continuous wave Doppler. The sensitivity of flow convergence in Carpentier-Edwards, St. Jude, and cage-ball valves was 80%, 73%, and 67%, respectively; whereas the sensitivity of left atrial color Doppler was 70%, 27%, and 0%, and the sensitivity of continuous wave Doppler was 33%, 0%, and 13%. Flow convergence was the only sign of significant regurgitation in 12 of 30 patients (40%); 10 of these patients had mechanical valves. We conclude flow convergence is a more sensitive, though less specific, predictor of significant mitral regurgitation than color Doppler, spatial mapping of the left atrium, and continuous wave Doppler, especially when a mechanical valve is present.