Background PKARI alpha (protein kinase A type I-alpha regulatory subunit) is redox-active independent of its physiologic agonist cAMP. However, it is unknown whether this alternative mechanism of PKARI alpha activation may be of relevance to cardiac excitation-contraction coupling. Methods and Results We used a redox-dead transgenic mouse model with homozygous knock-in replacement of redox-sensitive cysteine 17 with serine within the regulatory subunits of PKARI alpha (KI). Reactive oxygen species were acutely evoked by exposure of isolated cardiac myocytes to AngII (angiotensin II, 1 mu mol/L). The long-term relevance of oxidized PKARI alpha was investigated in KI mice and their wild-type (WT) littermates following transverse aortic constriction (TAC). AngII increased reactive oxygen species in both groups but with RI alpha dimer formation in WT only. AngII induced translocation of PKARI to the cell membrane and resulted in protein kinase A-dependent stimulation of I-Ca (L-type Ca current) in WT with no effect in KI myocytes. Consequently, Ca transients were reduced in KI myocytes as compared with WT cells following acute AngII exposure. Transverse aortic constriction-related reactive oxygen species formation resulted in RI alpha oxidation in WT but not in KI mice. Within 6 weeks after TAC, KI mice showed an enhanced deterioration of contractile function and impaired survival compared with WT. In accordance, compared with WT, ventricular myocytes from failing KI mice displayed significantly reduced Ca transient amplitudes and lack of I-Ca stimulation. Conversely, direct pharmacological stimulation of I-Ca using Bay K8644 rescued Ca transients in AngII-treated KI myocytes and contractile function in failing KI mice in vivo. Conclusions Oxidative activation of PKARI alpha with subsequent stimulation of I-Ca preserves cardiac function in the setting of acute and chronic oxidative stress.