Ventricular fibrillation is the most frequent persistent arrhythmia increasing mortality and morbidity. The main complication is ischemic stroke and systemic embolization. Silent brain infarctions and disorder of cognitive functions of non thrombolitic origin have been reported. Various stratifications of thrombolitic risk are used for selecting risk persons for primarily preventive antithrombolitic therapy. CHADS2 classification is the most frequent one. Patients with middle and high risk of thromboembolism are indicated for anticoagulation therapy, patients with middle and low risk are indicated for antiaggregation therapy. The study presents basic principles of stratification of thromboembolitic risk, anticoagulation therapy and control.