The authors propose a new method of operative intervention with instrumental transatrial mitral commissurotomy through a left-side transauricular approach by using a dilator on a flexible wire rope of a new design. The method was applied in surgery on 102 patients, aged from 18 to 56 yr. Of these 40.2 % (41) had stage IV of the affection and in 32 the operation was performed with the mitral valve in the state of calcinosis. In all of the patients a sufficiently large dilation of the mitral orifice, from 3 to 4.5 cm, could be achieved, the separation of both commissures having been effected in 91 (91.2%) of the patients. There were no complications due to the application of the dilator. One patient (0.9%) died in consequence of sepsis in the postoperative period. Late results were followed up in 75 patients over periods from 1 1/2 to 7 yr. In 69 (92%) these were held to be excellent and good. No recurrent stenosis and lethal outcomes late after surgery were on record. On the ground of positive results obtained by the authors they recommend employing the left-side transatrial commissurotomy on a flexible wire rope as an independent method of surgery in mitral stenosis which under a digital control ensures a highly effective commissurotomy with but minor traumatic lesion of the heart and minimal complications.