Electro-impulse therapy of atrial fibrillation in 627 patients with rheumatic mitral disease, atherosclerotic and myocardial cardiosclerosis proves the immediately high efficacy of the method. Dispensary examination of 455 patients revealed high rate of relapse of atrial fibrillation. A reverse relationship has been noted between the duration of the fibrillation and the duration of the sinus rhythm. The type of the main disease and the surgical treatment of the mitral disease produced no effect on the late results of electro-impulse therapy. The high rate of relapse of atrial fibrillation and the risk of complications demand strict selection of patients for this type of treatment.