Background - Atrial fibrillation ablation is often performed by achieving pulmonary vein isolation using the "wide antral circumferential ablation" (WACA) technique, but many pulmonary veins remain connected because of conduction gaps in the ablation line. Aim - To analyse the efficacy of a novel technique based on pacing manoeuvres to detect gaps in an initial WACA lesion. Methods - Patients referred for radiofrequency atrial fibrillation ablation were enrolled prospectively. A WACA lesion set was performed, isolating ipsilateral pulmonary veins together. If pulmonary vein isolation was not achieved, the atria were paced using an ablation catheter. For each pacing site, "activation delay" and "activation sequence" were analysed using a circular mapping catheter positioned at the pulmonary vein ostium. Results - Twenty-one patients were included. A total of 25 non-isolated WACA lesion sets were studied. Three patterns were identified: (1) the activation delays converged towards one point with the shortest delay; no modification of the activation sequence (indicating one gap); (2) the activation delays converged towards at least two close locations; no change in the activation sequence (indicating at least two close gaps); (3) the activation delays converged towards at least two remote locations; modification of the activation sequence (indicating at least two remote gaps). Pacing manoeuvres and effect of ablation allowed precise localization of gaps, ultimately leading to pulmonary vein isolation in all patients. Conclusion - This simple pacing method accurately detected the location of residual connections after WACA lesion sets performed for atrial fibrillation ablation, allowing pulmonary vein isolation to be achieved.