Significance The heart contracts more forcefully in response to fear, stress, or exercise through the fight-or-flight response. This physiological process is mediated by β-adrenergic receptors acting through adenylyl cyclase, cAMP, and cAMP-dependent protein kinase (PKA), which phosphorylates the cardiac calcium channel Ca V 1.2 and increases its activity. We show that mutation of a single amino acid residue, Ser-1700, in a PKA phosphorylation site at the interface between the distal and proximal C-terminal domains substantially disrupts this regulatory mechanism in mice. Basal and β-adrenergic–stimulated calcium currents, myocyte contractility, and stress-induced exercise capacity are all reduced. Moreover, these mice develop cardiac hypertrophy, an indication of failure of cardiac homeostasis in vivo. Evidently, phosphorylation of Ser-1700 is a primary event in cardiovascular regulation.