The optimal method to perform external electrical cardioversion of atrial fibrillation has not been fully determined yet. In order to define the effects of different pad positions on cardioversion success rates, shock energy requirements and serum myocardial proteins levels we studied 62 patients with persistent atrial fibrillation who underwent elective external electrical cardioversion using a standardized step-up protocol of increasing energy levels. Electrode positions were randomly assigned as anterolateral (Group A) or anteroposterior (Group B). After all shocks were delivered there was no difference in the cardioversion success rate between the two groups. However, a significantly greater proportion of patients in group B were restored to sinus rhythm after the second shock of 300 J was delivered (p=0.005). Mean shock energy requirements and peak serum creatine kinase levels were lower for group B than for group A (p=0.049 and p=0.021 respectively). Troponin T serum levels were not increased after the cardioversion attempts in either group. We conclude that an anteroposterior electrode position is more effective in achieving restoration of sinus rhythm in lower energy shock levels compared to the anterolateral position.