To determine the utility of transesophageal echocardiographic monitoring during percutaneous balloon mitral valvotomy, we analyzed data from 40 consecutive patients who had been randomly assigned to undergo balloon mitral valvotomy under transesophageal echocardiographic guidance or without echo. All procedures were carried out under general anaesthesia. The completion rate (100% vs 73%), the procedure time (108 +/- 28 min vs 65 +/- 18 min), the X-ray exposure time (62 +/- 13 vs 33 +/- 12 min), resulted significantly (P less than 0.001) more favorable in the echo-monitored patients. Moreover, a lower rate of major complications (cardiac tamponade, large residual atrial shunting, and severe mitral regurgitation) was noted in the echo-monitored patients. The achieved final area of the mitral valve did not differ significantly between the two groups. From an evaluation of results as a whole, 96% of the echo-monitored procedures were successful, whereas only 40% of the procedures conducted without echocardiographic control achieved a satisfactory final result in absence of major complications. We conclude that transesophageal echocardiography is a safe, effective, and valuable tool to monitor each step of balloon mitral valvotomy in order to shorten the time of the procedure, and to improve the results of this complex interventional catheterization technique.