Background: Intermediate-conductance calcium-activated potassium channels (KCa3.1) are important for automaticity of sinus nodes. Previous studies have identified that cardiomyocytes with pacemaker activities are existent in pulmonary vein (PV), superior vena cava (SVC). The aim of the present study was to explore the electrophysiological characteristics and differential densities of KCa3.1 in rabbit atrium. Methods: Immune-staining techniques and western blots were used to determine the KCa3.1 expression in PV, SVC, right atrium (RA), and left atrium (LA). Transmembrane action potentials (APs) of PVs, SVC, RA, and LA were recorded. Isoproterenol (1uM) and high calcium (5.4mM) were used to induce delayed afterdepolarization (DAD) and DAD-induced trigger activity. Results: The expression of KCa3.1 was significantly higher in the PVs and SVC than in the RA and LA. After super-fusion with isoproterenol (1μM) and high calcium (5.4mM), the delayed afterdepolarization (DAD) and DAD-induced triggered activity was induced in the PVs and SVC, but not in the RA and LA with isoproterenol and high calcium administration. TRAM-34 (5uM), a KCa3.1 inhibitor, inhibited DAD and DAD-induced triggered activity. Conclusions: Compared with atrium, thoracic veins are the most common sites genesis AF due to different distribution of KCa3.1. Blockade of KCa3.1 could eliminate DAD and DAD-induced trigger activity, KCa3.1 might be a promising target for foci AF.