["Temporary, ablation-mediated effects such as oedema may cause reversible pulmonary vein (PV) isolation. To investigate this, point-by-point circumferential ablation was performed to achieve acute electrical PV isolation with an incomplete circumferential ablation line. Then, the impact of this intentional 'visual gap' (ViG) on the conduction properties of the ablation lesion set was assessed with adenosine and pacing manoeuvres.", 'Twenty-eight patients undergoing ablation for paroxysmal (n= 20) or persistent atrial fibrillation (n= 8) were included. Pulmonary vein (PV) ablation was performed around ipsilateral vein pairs. Once acute isolation was achieved, ablation was halted and the presence and size of the ViG were calculated. The ViG electrophysiological properties were tested with pace capture along the ViG at 10 mA/2 ms, and assessment for dormant PV conduction with adenosine. Despite electrical isolation, a ViG was present in 75% (n= 42/56) of vein pairs (21 of 28 left PVs and 21 of 28 right PVs). There was no difference in the ViG size between the left and right PVs (22.1 ± 14.2 and 17.3 ± 11.3 mm, P > 0.05). Dormant PV connections were revealed by adenosine in more than a quarter (n= 12/42) of acutely isolated PV pairs, of which the majority were dependent on conduction through the ViG.'] Is acute electrical isolation a necessary but insufficient endpoint for achieving durable PV isolation : the importance of closing the visual gap?