It is hypothesised that a dual therapy strategy by oral anticoagulation with the new Factor-Xa-inhibitor apixaban plus clopidogrel is superior to a triple therapy regimen with phenprocoumon plus acetylsalicylic acid (ASA) and clopidogrel with respect to avoiding bleeding events in patients with atrial fibrillation undergoing percutaneous coronary intervention in the setting of an acute coronary syndrome.