Atrial fibrillation (AF) is a frequent reason for emergency department visits. According to current guidelines either rate- or rhythm-control are acceptable therapeutic options in such situations. In this report, we present the complicated clinical course of a patient with AF and a rapid ventricular response. Because of paroxysmal AF, the patient was on chronic oral anticoagulation therapy with warfarin. Pharmacological treatment was ineffective to control ventricular rate, and immediate synchronized electrical cardioversion was performed. One hour later, the patient complained of chest pain in combination with marked ST-segment elevation in the anterior leads. Cardiac catheterization with optical coherence tomography disclosed plaque rupture in the left main coronary artery without other significant stenosis. Stent implantation was performed successfully. During the course of the hospital stay, the patient remained asymptomatic and the ST-segment elevations resolved. However, despite treatment with amiodarone it was not possible to keep the patient permanently in sinus rhythm. Therefore, a biventricular pacemaker was implanted and AV node ablation performed.