Patients with atrial fibrillation (AF) presenting an acute coronary syndrome (ACS) and undergoing PCI require a triple therapy with a combination of oral anticoagulation (OAC) and dual anti-platelet therapy. Current guidelines recommend a regimen consisting of aspirin, clopidogrel and an oral anticoagulant. Although effective in preventing recurrent ischemia, triple therapy confers an elevated bleeding risk, which also has a major impact on the patients' prognosis and survival. Data from one randomized trial suggest that omitting aspirin in patients with indication for triple therapy may reduce the risk of bleeding without an increase of the rate of ischemic events. In addition, the recently introduced non-vitamin-K oral anticoagulants (NOACs) show less bleeding events as compared to vitamin-K antagonist in AF patients. In this trial it is postulated that a dual therapy consisting of the factor-Xa inhibitor apixaban and clopidogrel is associated with significant lower bleeding rates as compared to traditional triple therapy with aspirin, clopidogrel and a vitamin K antagonist (VKA). To test this hypothesis, patients with atrial fibrillation, who underwent PCI in the setting of an ACS will be randomized to either a dual therapy (apixaban+clopidogrel) or a triple therapy (aspirin+clopiodgrel+VKA). The patients will be followed-up for 6 months after randomization.