Rationale: Multiple cyclic nucleotide phosphodiesterases (PDEs) degrade cAMP in cardiomyocytes but the role of PDEs in controlling cAMP signaling during pathological cardiac hypertrophy is poorly defined. Objective: Evaluate the β-adrenergic regulation of cardiac contractility and characterize the changes in cardiomyocyte cAMP signals and cAMP-PDE expression and activity following cardiac hypertrophy. Methods and Results: Cardiac hypertrophy was induced in rats by thoracic aortic banding over a time period of 5 weeks and was confirmed by anatomic measurements and echocardiography. Ex vivo myocardial function was evaluated in Langendorff-perfused hearts. Engineered cyclic nucleotide-gated (CNG) channels were expressed in single cardiomyocytes to monitor subsarcolemmal cAMP using whole-cell patch-clamp recordings of the associated CNG current (ICNG). PDE variant activity and protein level were determined in purified cardiomyocytes. Aortic stenosis rats exhibited a 67% increase in heart weight compared to sham-operated animals. The inotropic response to maximal β-adrenergic stimulation was reduced by 54% in isolated hypertrophied hearts, along with a 32% decrease in subsarcolemmal cAMP levels in hypertrophied myocytes. Total cAMP hydrolytic activity as well as PDE3 and PDE4 activities were reduced in hypertrophied myocytes, because of a reduction of PDE3A, PDE4A, and PDE4B, whereas PDE4D was unchanged. Regulation of β-adrenergic cAMP signals by PDEs was blunted in hypertrophied myocytes, as demonstrated by the diminished effects of IBMX (100 μmol/L) and of both the PDE3 inhibitor cilostamide (1 μmol/L) and the PDE4 inhibitor Ro 201724 (10 μmol/L). Conclusions: β-Adrenergic desensitization is accompanied by a reduction in cAMP-PDE and an altered modulation of β-adrenergic cAMP signals in cardiac hypertrophy.