IK1 inhibitor PA-6 (PA-6), a pentamidine analogue, is a selective and potent IK1 (KIR2.x ion-channel-carried inward rectifier current) inhibitor, with IC50 values of 12-15 nM for human and mouse KIR2.x currents. IK1 inhibitor PA-6 (PA-6) elevates KIR2.1 protein expression and induces intracellular KIR2.1 accumulation. IK1 inhibitor PA-6 (PA-6) has the potential to treat atrial fibrillation and arrhythmia.