Organized activity of the myocardium manifested in dominant frequency structure of EСG was typical of the first 10 min of ventricular fibrillation in canine heart. The first minute of fibrillation was characterized by the most pronounced changes in the structure of oscillation frequency and transition from domination of high frequency oscillations (13-17 Hz) to domination of medium (8-12 Hz) and then low frequency (4-7 Hz) oscillations. The second minute was characterized by transition from domination of low frequency oscillations to domination of low and medium frequency oscillations; minutes 3-10 were characterized by domination of low and medium frequency oscillations; after 10 min, non-dominant ventricular oscillations were recorded.