Background: Multiple atrial tachycardias (ATs) in one patient usually require more complex ablation procedures. Despite the superior accuracy and understanding of conduction features provided by high-resolution mapping, Multiple ATs are still associated with high recurrence rates, and other mechanisms may play a role. Therefore, we aimed to uncover the substrates maintaining these multiple reentrant circuits and the probable mechanisms for the high occurrence of arrhythmia. Methods: Mapping via the Carto system was carried out in 8 patients with more than two types of reentrant circuits during ablation. Functional conduction block (FCB) regions were marked and further analyzed. Results: Twenty sustained ATs were mapped in the 8 patients. Five of these patients exhibited a potential FCB region that changed between different ATs. The potentials of these regions converted between double potentials (DPs), fractionated potentials (FPs) and normal potential due to the different ATs. The FCB regions were the main obstacles and the center of the reentrant circuit in 8 of 14 ATs, and in the other ATs, these regions played a role in reorganizing the conduction pathway. In the activation mapping, the FCB areas were never the target ablation site. Conclusion: The potential FCB region is common in ATs with more than two types of reentrant circuits, especially in scar-related localized reentry. The convertibility of FCB regions provide one of the critical substrates in maintaining multiple ATs. The changefulness of this substrate may be one of the important causes of the high recurrence of related ATs