Verapamil hydrochloride is an L-type calcium channel antagonist. IC50 & Target: Calcium channel^[1] In Vitro: Verapamil (hydrochloride) is an L-type calcium channel antagonist. The combination of Bortezomib and Verapamil (70 µM) markedly declines the viability of the JK-6L, RPMI 8226, and ARH-77 cell lines after 16 hours of culture^[1]. The enzyme hydrolase activity of recombinant human carboxylesterase (CES2) is substantially inhibited by Verapamil with K_i of 3.84±0.99μM^[2]. In Vivo: Verapamil, a calcium channel antagonist, is injected i.v. into a femoral vein prior to ischemia. Verapamil (1 mg/kg) significantly decreases the incidence of ventricular arrhythmias including premature ventricular contractions (PVC), ventricular tachycardia (VT) and ventricular fibrillation (VF) for 45-min coronary artery occlusion. Total arrhythmia scores are significantly increased when the heart is subjected to ischemia (P<0.01 vs. sham). Verapamil (1 mg/kg) significantly prevented the enhancement of total arrhythmia scores induced by ischemia (P<0.01 vs. ischemia). Results indicate that Verapamil exerts an anti-arrhythmic property^[3].