Previously, a non-escalating protocol (200 J) (5) has been found to have a significantly higher first shock success resulting in fewer shock deliveries without compromising safety compared with a low energy escalating shock protocol (100-150-200 J). Further, a study found fewer arrhythmic complications with increasing energy suggesting an 'upper limit of vulnerability'. It is well-established that biphasic shocks induce fewer post-shock arrhythmias (6), skin burns (7) and shorter periods of myocardial stunning compared with monophasic shocks.(8) Importantly, no correlation between increasing biphasic energy delivery and any complications was found in these studies. Nonetheless, the efficiency and safety of a high energy shock (360 J) biphasic protocol compared with a conventional low energy escalating protocol is unknown. Accordingly, this study aims to compare the efficiency and safety of a high energy protocol (360-360-360 J) versus a standard escalating protocol (125-150-200 J). We hypothesise that a high energy cardioversion protocol is more effective compared to standard escalating energy protocol, without compromising safety.