The purpose of this study was to evaluate the potential advantages of on-line transesophageal echocardiography during percutaneous balloon mitral valvuloplasty (PBMV). One hundred thirty-four consecutive patients who underwent PBMV were included in this study. Group 1 included 64 patients who underwent PBMV under fluoroscopy guide only, and group 2 included 70 patients who underwent PBMV under on-line transesophageal echocardiography guide. Inoue balloons were used in all cases. The mitral valve area after valvuloplasty was comparable between the 2 groups. The procedure time was significantly shorter in group 2 (99 ± 48 min vs 64 ± 22 min, P < .0001), and the average fluoroscopy time was shorter in group 2 without statistical significance (30 ± 17 min vs 19 ± 15 min, P = .25). Five (7.8%) patients in group 1 and 2 (2.8%) patients in group 2 underwent surgery because of procedure-related complications. The limitation of this study was the learning curve of the operator, because the 2 groups were treated serially. In conclusion, transesophageal echocardiography can be used effectively during balloon mitral valvuloplasty, and it may help to reduce the rate of complications resulting from trans-septal catheterization and balloon valvuloplasty and to reduce procedure time and fluoroscopy time.