A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was how many cardioversion attempts should be performed for patients who have gone into ventricular fibrillation post-cardiac surgery prior to performing chest reopening. Using the reported search, 1183 papers were identified. Fifteen papers represented the best evidence on the subject. The author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results and study comments and weaknesses were tabulated. The quality and level of evidence was assessed using the International Liaison Committee of Resuscitation guideline recommendations. The most recent European Resuscitation Council guidelines suggest single attempts at cardioversion, spaced at 2-min intervals, for all patients going into ventricular fibrillation or pulseless ventricular tachycardia. Cardiac surgery presents a unique challenge for these guidelines in that emergency re-sternotomy may provide additional lifesaving interventions once it is deemed that external cardioversion is unlikely to succeed. The 15 papers identified demonstrated that the success of the first attempt at cardioversion for VF/VT was around 78%. The chance of the second shock succeeding was around 35%. The chance of a third shock succeeding was 14%. Very little data were found on the chance of further shocks succeeding. Of note none of these papers were in patients on the intensive care after cardiac surgery. We conclude that, due to the importance of minimising the delay to chest reopening, three shocks should be quickly delivered. If these do not succeed the chance of a 4th shock succeeding is likely to be <10% and, thus, immediate chest reopening should be performed. (This is a Class-IIa recommendation using ILCOR guideline recommendations.).