Recurrences of atrial fibrillation (AF) after radiofrequency catheter ablation (RFCA) are usually caused by pulmonary vein (PV) re-conduction, by foci outside the PV or by previous electrical remodelling. Substrate alterations with conduction delays may be detected by signal-averaged P-wave analysis (SAPW). This study was conducted to assess the value of the SAPW to predict recurrences after RFCA in patients with paroxysmal or persistent AF.