Hypothesis:

Blocking the angiotensin (AT) II type 1 receptor (Olmesartan) reduces the incidence of episodes of atrial fibrillation in patients with paroxysmal atrial fibrillation during 12 months by more than 25% compared to standard medication without angiotensin II type 1 receptor.

A total of 422 subjects will be included in the two study groups. The treatment arm will receive 40mg Olmesartan per day, the remaining patients will receive placebo. Follow-up is 12 months. Daily Tele-ECG recordings will determine the cardiac rhythm and asymptomatic episodes of atrial fibrillation (AF) every day. Concomitant therapy with AV-nodal blocking drugs are allowed during the study. In case of severe AF-induced symptoms, an antiarrhythmic "recovery medication" (amiodarone) is allowed during follow-up.

Double-blind, central randomization, two treatment groups, stratified by beta-blocker use. 211 patients in each treatment arm.

Inclusion Criteria:

• Documented paroxysmal atrial fibrillation: ECG documentation of atrial fibrillation at least in one ECG recorded during the last 2 months prior to randomization plus additional ECG recording of sinus rhythm at least 12 hours after the above mentioned ECG documentation.
• Age ≥ 18
• Patient informed orally and in writing
• Written informed consent of the patient

Exclusion Criteria:

• Strong clinical evidence for therapy with AT II/ACE inhibitors
• AT II/ACE inhibitor therapy within the last month
• Therapy with antiarrhythmic agents of class I or class III within the last month, therapy with amiodarone within the last 3 months
• Direct current (DC) cardioversion within the last 3 months
• Symptomatic bradycardia
• Implanted pacemaker or implanted cardioverter/defibrillator with any antitachycardiac algorithm in use
• Cardiac surgery or cardiac catheter ablation within the last 3 months
• Typical angina pectoris symptoms at rest or during exercise
• Known coronary artery disease with indication for intervention
• Valvular disease > II degree
• Left ventricular ejection fraction < 40%
• Diastolic blood pressure > 110mm Hg at rest
• Symptomatic arterial hypotension
• Known renal artery stenosis
• Serum creatinine > 1.8 mval/l
• Relevant hepatic or pulmonary disorders
• Hyperthyroidism manifested clinically and in laboratory
• Known drug intolerance for AT II inhibitors
• Females who are pregnant or breast feeding
• Females of childbearing potential who are not using a scientifically accepted method of contraception
• Participation in a clinical trial within the last 30 days
• Drug addiction or chronic alcohol abuse
• Legal incapacity, or other circumstances which would prevent the patient from understanding the aim, nature or extent of the clinical study
• Evidence of an uncooperative attitude