Atrial fibrillation is associated with three major risk of complications: thromboembolism, hemodynamic compromise, and arrhythmogenesis. In patients with chronic atrial fibrillation the incidence of embolization is about 5% per year. The risk of embolism and in particular of stroke can be reduced by warfarin anticoagulation. Aspirin is generally less effective than warfarin, although it is probably more effective than placebo. The hemodynamic complications which may occur during atrial fibrillation are mainly due to the loss of effective atrial contraction, the irregular ventricular rhythm, and the possible excessively rapid ventricular rate. Sudden death is a recognized manifestation of Wolff-Parkinson-White syndrome and is considered to be precipitated by atrial fibrillation in the majority of patients. Torsades de pointes is perhaps the most widely recognized proarrhythmia associated with treatment of atrial fibrillation, especially with 1A antiarrhythmic drugs and sotalol. The chronic treatment with type 1C drugs in 3.5%-5% of patients may induce atrial flutter with 1:1 conduction with significant hemodynamic compromise.