Patients with atrial fibrillation or flutter for ≤48 hours may be cardioverted immediately. Patients with atrial fibrillation or flutter for >48 hours will be required to have a documented weekly international normalized ratio (INR) ≥2.0 (including within 48 hours of cardioversion) or treatment with dabigatranetexilat for three weeks or longer. Alternatively, a transoesophageal echocardiogram documenting absence of intracardiac thrombi is accepted and cardioversion can be performed on treatment with low molecular weight heparin. All patients will be discharged with a recommendation for therapeutic anticoagulation according to current guidelines.