Ang II receptor activation increases cytosolic Ca²⁺ levels to enhance the synthesis and secretion of aldosterone, a recently identified early pathogenic stimulus that adversely influences cardiovascular homeostasis. Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is a downstream effector of the Ang II–elicited signaling cascade that serves as a key intracellular Ca²⁺ sensor to feedback-regulate Ca²⁺ entry through voltage-gated Ca²⁺ channels. However, the molecular mechanism(s) by which CaMKII regulates these important physiological targets to increase Ca²⁺ entry remain unresolved. We show here that CaMKII forms a signaling complex with α_1H T-type Ca²⁺ channels, directly interacting with the intracellular loop connecting domains II and III of the channel pore (II-III loop). Activation of the kinase mediated the phosphorylation of Ser1198 in the II-III loop and the positive feedback regulation of channel gating both in intact cells in situ and in cells of the native adrenal zona glomerulosa stimulated by Ang II in vivo. These data define the molecular basis for the in vivo modulation of native T-type Ca²⁺ channels by CaMKII and suggest that the disruption of this signaling complex in the zona glomerulosa may provide a new therapeutic approach to limit aldosterone production and cardiovascular disease progression.