To evaluate mitral valve function and its long-term outcome after open mitral commissurotomy (OMC), we examined 39 patients using Doppler echocardiography. There were 13 males and 26 females; who were examined a total of 83 times after the surgery at about one year intervals (seven to 240 months, averaging 78 months). We measured the velocity of transmitral blood flow using the continuous wave Doppler method (CWD), and the transmitral pressure half time (PHT), mean velocity (m V) and peak velocity (pV) were calculated. The presence and severity of mitral regurgitation (MR) were assessed by color flow mapping. 1. PHT gradually increased and significantly correlated (r = 0.63, p less than 0.001) with the months passed after OMC. The regression line of PHT in postoperative months was "PHT = 0.70 x PMo + 83" (PMo = postoperative months). The mV and pV tended to increase gradually, but did not significantly correlate with the months passed after the surgery. 2. Among the 39 patients, 28 (72%) had MR, and their severity was classified as 1+ in two, 2+ in 19, 3+ in six and 4+ in one. Among 21 patients who had no MR before OMC, MR appeared in 12 (57%), and its severity was classified as 1+ in one, 2+ in nine and 3+ in two. All five patients with preoperative MR had MR postoperatively, and their severity was classified as 1+ in one, 2+ in two and 3+ in two. The presence of the preoperative MR of the remaining 13 patients was unknown.(ABSTRACT TRUNCATED AT 250 WORDS)