From 1982 to the late 1990 thirty-three patients with tachysystolic atrial fibrillation refractory to preventive antiarrhythmic therapy were examined and operated on. Invasive electrophysiological investigation was a must in the preoperative examination. The "entrainment" and "adaptation" effects of the refractory periods of different parts of the atria were estimated depending on the duration of the basic cycle of pacing. After provoking atrial flutter paroxysm the place of the early appearance of A spike was determined and endocardial mapping was performed. During intraoperative mapping, the data of low-amplitude and fragmented activity were processed by a computer; the sequence of electric activation of the atria was determined on flutter. 20 transthoracic operations with extracorporeal circulation were made. Of these, there were 7 operations of laser or cryogenic isolation of the AB node, 30 of laser photo ablation, and 9 of cryodestruction of the arrhythmogenic areas. In a female patient, resection of the terminal crest and sinoatrial node followed by implantation of a pacemaker was performed in the AAI mode. Closed operations involved both transvenous electrodestruction of the arrhythmogenic areas (5 patients) and destruction of the His bundle with the development of complete transverse block and implantation of the pacemaker in the VVI mode. The best results were attained in young persons with Type I idiopathic atrial flutter where areas of fragmented and low-amplitude activity could be accurately specified.