To clarify the clinical significance of the intraoperative monitoring for mitral valve repair by transesophageal echocardiography (TEE), we evaluated the correlation of color Doppler flow area of residual mitral regurgitation (residual MR area) between intraoperative and postoperative TEE. Subjects were 12 patients (average age was 54.7 years) underwent recently intraoperative TEE. These 12 patients were divided into two groups: Group A (MR area < 2.0 cm2; n = 8) and Group B (MR area > 2.0 cm2; n = 4). None of the 12 patients required second pump run. In all cases, residual MR area, as determined using intraoperative TEE, was less than 3.2 cm2. One month after surgery, the MR area did not showed an increase in Group A, while in Group B it decreased slightly in 2 cases, remained unchanged in 1 case and increased slightly in 1. Our findings do not support the usefulness of intraoperative monitoring with TEE. It seems difficult to predict the outcome of residual MR on the basis of the MR area alone. At present, we thought that, possibly, intraoperative monitoring with TEE is indispensable for mitral valve repair. A longer follow-up will be necessary to draw firm conclusions.