A large variety of parameters have been proposed for quantification of atrial fibrillation substrate complexity computed on a standard 12-lead ECG. A direct comparison of the predictive performance of these complexity parameters using a single dataset has not been performed. We retrospectively studied 221 patients undergoing pharmacological cardioversion (CV) with flecainide to compare the predictive performance of dominant atrial frequency (DF), spectral organization index (OI), spectral entropy (SE), sample entropy (SampEn) and fibrillation wave amplitude (FWA).