AP14145 hydrochloride is a potent negative allosteric modulator of K Ca 2 (SK) channels, specifically targeting K Ca 2.2 (SK2) and K Ca 2.3 (SK3) channels with an IC 50 of 1.1 μM. Inhibition of AP14145 hydrochloride is highly influenced by S508 and A533 amino acids present in the channel. This compound effectively extends the atrial effective refractory period (AERP) in rats and exhibits antiarrhythmic properties in a Vernakalant-resistant porcine model of atrial fibrillation (AF).