The optimal energy selection for biphasic direct current (DC) cardioversion of atrial fibrillation is unknown. The energy delivered should be sufficient to achieve prompt cardioversion but without the risk of inducing any potential injury e.g. skin burns, myocardial stunning or post-cardioversion arrhythmias. The use of an escalating protocol, with a low energy initial shock, has been considered conventional practice, originally to avoid post cardioversion arrhythmias when using monophasic shocks.(1) This practice has been directly transferred to biphasic cardioversion. The European Society of Cardiology 2016 guidelines (2) and the American Heart Association/American College of Cardiology 2014 guidelines on the management of atrial fibrillation (3) do not recommend any specific energy settings, whereas the European Resuscitation Council 2010 guidelines for cardiopulmonary resuscitation (4) recommend a starting energy level of 120-200 J with subsequent escalating energy setting.