L-type Ca2+ channels (LTCCs) are major entry points for Ca2+ in many cells. Ca2+/calmodulin-dependent protein kinase II (CaMKII) is associated with cardiac LTCC complexes and increases channel open probability (PO) to dynamically increase Ca2+ current (ICa) and augment cellular Ca2+ signaling by a process called facilitation. However, the critical molecular mechanisms for CaMKII localization to LTCCs and ICa facilitation in cardiomyocytes have not been defined. We show CaMKII binds to the LTCC b2a subunit and preferentially phosphorylates Thr498 in b2a. Mutation of Thr498 to Ala (T498A) in b2a prevents CaMKII-mediated increases in the PO of recombinant LTCCs. Moreover, expression of b2a (T498A) in adult cardiomyocytes ablates CaMKII-mediated ICa facilitation, demonstrating that phosphorylation of b2a at Thr498 modulates native calcium channels. These findings reveal a molecular mechanism for targeting CaMKII to LTCCs and facilitating ICa that may modulate Ca2+ entry in diverse cell types coexpressing CaMKII and the b2a subunit.