Blood samples, ECG, blood pressure, oxygen saturation and heart rate will be obtained at baseline and all patients will receive 0.5 mg Rapifen i.v. All patients will be treated with 100 % oxygen or room air, 10-15 L/ minute for 3 minutes before administration of Propofol. All patients will be treated with Propofol 1 mg i.v./kg bodyweight with subsequent 20 mg boluses as needed. Before cardioversion PaO2 will be measured by arterial blood gas (1 mL).