Regurgitant blood flow of mitral valves was studied by transesophageal Doppler color flow echocardiographic imaging in 11 healthy volunteers (Group 1), 25 cardiac patients with a native mitral valve (Group 2), 10 patients with a normally functioning Björk-Shiley mitral prosthesis without clinical evidence of mitral regurgitation (Group 3) and 10 patients with angiographic or surgical evidence of Björk-Shiley mitral valve regurgitation (Group 4). Holosystolic regurgitant color jets were classified as type I or type II. The data were compared with results obtained with precordial techniques, i.e., continuous wave and Doppler color flow echocardiographic imaging (Groups 1 to 4) and left ventricular angiography or surgery (Groups 2 and 4). In Group 1, transesophageal Doppler color flow imaging revealed no mitral regurgitant flow in 7 of the 11 patients and a type I jet in 4 patients that was detected in only 1 patient by precordial techniques. In Group 2, angiography showed no mitral regurgitation in 20 patients and documented mitral regurgitation in 5. Transesophageal Doppler color flow imaging detected in 4 of the 20 patients a type I jet that was not visualized with precordial techniques in 2 patients. Type II jets were detected by the transesophageal technique in all five patients with proven mitral regurgitation and were also visualized with precordial echocardiography. All patients in Group 3 showed two identical type I jets that were not detected with precordial echocardiography.(ABSTRACT TRUNCATED AT 250 WORDS)