Background: The effect of circumferential pulmonary vein isolation (CPVI) with both roof line and posterior line and additional Bachmann bundle block (BBB) on P wave characteristics is not unknown. Aims: To assess the influence of staged left atrial isolation on P wave changes. Methods: Twenty four patients (58짹14 yrs, 17 males) underwent CPVI with both roof and posterior line and anterior line for non-paroxysmal atrial fibrillation. P wave duration and peak p wave voltage were measured at the start of procedure and after CPVI with both roof and posterior line and end of Bachmann bundle block. Results: P wave duration increased from 144짹27 ms to 149짹28 ms after CPVI and both roof and posterior line and eventually to 166짹33 ms after BBB (p=0.09). Significant peak p wave voltage increase was seen in lead V1 (0.08짹0.03 mV vs.0.11짹0.03 mV vs. 0.11짹0.04 mV, p=0.0034). Peak p wave voltages showed increased tendency after ablation procedure in lead V1,V2 and V3 and decreased tendency in lead V5 and V6 (Table 1). Conclusion: CPVI with both roof and posterior line and Bachmann bundle block results in increased p wave duration and and p wave volatage gain in precordial lead V1,2,3 and voltage loss in lead V5,6.