The initial therapy of atrial fibrillation is guided by the clinical symptomatology of the patient. Acute atrial fibrillation at a rapid ventricular rate is an emergency situation. Pharmacological therapy is aimed to delay atrioventricular conduction and thereby slow the ventricular rate. A new and interesting therapeutical option to induce conversion to sinus rhythm is the intravenous administration of classic drugs. The conversion rate of patients with nonvalvular atrial fibrillation of recent onset is high and accounts up to 90%. Patients with atrial fibrillation have an increased incidence of ischemic stroke. Anticoagulation, i.e. administration of aspirin in patients under 70 years of age, can reduce the occurrence of cerebral ischemic event.