FPL64176 is a nondihydropyridine agonist of Cav1.2 Ca²⁺ channels. Although it is very potent and efficacious, the molecular mechanism underlying its action has not been unequivocally identified. Because it was previously proposed that it may augment the channel currents by making inactivated channels permeable, we here examined its effect on recombinant Cav1.2 Ca²⁺ channels (alpha_1C/beta_2a/alpha₂delta₁) bearing mutations impairing different types of inactivation. Voltage-dependent inactivation (VDI) caused by a cytoplasmic linker between domains I and II of alpha_1C subunits was inhibited by a mutation causing Timothy syndrome 1, whereas VDI caused by a distal C-terminus (DCT) of alpha_1C subunits was inhibited by deletion of DCT. Ca²⁺-induced inactivation (CDI) caused by the binding of Ca²⁺ to calmodulin (CaM) preassociated with an IQ domain in the proximal C-terminus (PCT) of alpha_1C subunits was inhibited by coexpression of dominant negative CaM. We found that FPL64176 augmented the channel currents depending on CaM-mediated CDI and DCT-mediated VDI. It is known that the EF-hand in PCT is involved in both these types of inactivation. Therefore, it is likely that FPL64176 allosterically modulates the regulation of EF-hand by DCT and PCT associated with Ca²⁺/CaM.