A total of 381 persons belonging to the most seriously affected population of patients with mitral stenosis were operated upon from the dextral transatrial approach by using dilators on a flexible wire. Among these were also 89 patients with mitral restenosis and 58with mitral-tricuspidal stenosis. Patients presenting a high risk of developing thromboembolic complications comprised 72.9 per cent of the total number. The operations were attended by a minimum number of complications, with the overall lethality amounting to 2.5 per cent. In cases of mitral restenosis it was brought down to 1.1 and in those of mitral-tricuspidal stenosis, down to 1.7 per cent. Most of the lethal outcomes were due to an extremely grave initial condition of the patients subjected to surgery. Two (0.5 per cent) patients succumbed on account of thromboembolisms. The results obtained differ from average figures for lethality and complications in analogous groups of patients operated upon with application of other methods. They allow the transatrial mitral commissurotomy with a dilator on a flexible wire executed from the dextral approach consider to be a simple, effective and little-traumatic method of surgical correction of the gravest forms of mitral stenosis, mitral restenosis and mitral-tricuspidal stenosis. The method deserves to be applied broadly in the clinical practice of cardiosurgical establishments.