 Atrial fibrillation AF is the most common cardiac arrhythmia with a prevalence of 1-2. Without antithrombotic treatment, the annual risk of a cardioembolic event is 5-6. The source of a cardioembolic event is a thrombus, which usually forms in the left atrial appendage LAA. The prevention of cardioembolic events involves treatment with anticoagulant drugs, which were limited to, until recently, vitamin K antagonists e.g. warfarin. Anticoagulant treatment with warfarin can lead to adverse bleeding events, some of which can be life threatening. Recently, two new options for thrombus prevention have been developed. The first is the novel anticoagulants NOAC, which were associated with slightly better safety profiles due to a lower frequency of intracranial bleeding in large randomized trials . The second option involves interventional occlusion of the LAA. The aim of this project is to compare the LAA occlusion intervention to NOAC pharmacological treatment in a randomized multicenter study of AF patients at high risk of a cardioembolic event. 