The cyclic nucleotides cAMP and cGMP play important roles in mediating both protective and detrimental signaling in heart failure. By acting as regulators of cAMP and cGMP, the phosphodiesterases play important roles in modulating this signaling. A comparison of PDE expression between control mice and mice given transverse aortic constriction revealed that expression of phosphodiesterase 1C (PDE1C) was increased significantly by TAC, both on the mRNA and protein levels. To determine whether this was protective or maladaptive, we performed TAC on mice with a genetic deletion of PDE1C. While TAC-operated WT mice experienced significant overall cardiac hypertrophy and cardiomyocyte hypertrophy, these were reduced in PDE1C KO mice. Cardiac function, as assessed by echocardiography, was also reduced significantly in WT TAC mice, but was preserved in PDE1C KO TAC mice. Histological analysis indicated that TAC-operated PDE1C KO mice also experienced reduced cardiomyocyte apoptosis compared to WT mice, indicating a potential cardioprotective mechanism for PDE1C deletion. Cardiomyocytes isolated from PDE1C KO mice experienced reduced Ang II or Iso-induced cell death compared to WT myocytes, indicating that this was a cardiomyocytes-specific effect of PDE1C deletion. Ang II-induced cardiomyocyte cell death and apoptosis were also blocked via pharmacological PDE1 inhibition. PDE1C is able to hydrolyze either cAMP or cGMP; therefore, it seemed possible that this protective mechanism was dependent on either PKA- or PKG-mediated signaling. While PKG inhibition did not alter the protective effect of PDE1 inhibition in isolated cardiomyocytes, PKA inhibition blocked it. Overexpression studies also indicated that PDE1C is localized to the cell membrane in cardiomyocytes. Therefore, we propose that by modulating a novel, membrane-localized, anti-apoptotic, cAMP/PKA-dependent pathway in cardiomyocytes, PDE1C potentially represents a novel therapeutic target in heart failure.