Transesophageal Doppler echocardiography (TEDE) was performed to determine the incidence of physiological mitral regurgitation (MR) and the characteristics of regurgitant blood flow in presumably normal subjects. TEDE included color flow mapping, pulsed Doppler echocardiography and M-mode color flow mapping. Sixty-six surgical patients who had no histories or physical evidence of cardiac abnormalities were studied using TEDE under general anesthesia. MR flow was detected in 94% (62/66) of the patients by transesophageal color flow mapping. Transesophageal color flow mapping clearly differentiated physiological MR flow and signals generated from mitral valve closure. In 40% (25/62) of the patients whose MR flow was detected, transesophageal pulsed Doppler echocardiography (TEPD) revealed regurgitant signals lasting less than half of systole. Only 31% (19/62) had peak MR flow velocities greater than 1 m/sec. TEPD could not detect high velocities reflecting the pressure gradients across the mitral valve. Since the regurgitant volume was very small, TEPD may have been incapable of detecting high velocity components of the MR flow. In conclusion, our data suggested that nearly all normal subjects may have mild mitral regurgitation.