Cardiac atrial natriuretic peptide (ANP) locally counteracts cardiac hypertrophy via the guanylyl cyclase-A (GC-A) receptor and cGMP production, but the downstream signalling pathways are unknown. Here, we examined the influence of ANP on beta-adrenergic versus Angiotensin II (Ang II)-dependent (G(s) vs. G(alphaq) mediated) modulation of Ca(2+) (i)-handling in cardiomyocytes and of hypertrophy in intact hearts. L-type Ca(2+) currents and Ca(2+) (i) transients in adult isolated murine ventricular myocytes were studied by voltage-clamp recordings and fluorescence microscopy. ANP suppressed Ang II-stimulated Ca(2+) currents and transients, but had no effect on isoproterenol stimulation. Ang II suppression by ANP was abolished in cardiomyocytes of mice deficient in GC-A, in cyclic GMP-dependent protein kinase I (PKG I) or in the regulator of G protein signalling (RGS) 2, a target of PKG I. Cardiac hypertrophy in response to exogenous Ang II was significantly exacerbated in mice with conditional, cardiomyocyte-restricted GC-A deletion (CM GC-A KO). This was concomitant to increased activation of the Ca(2+)/calmodulin-dependent prohypertrophic signal transducer CaMKII. In contrast, beta-adrenoreceptor-induced hypertrophy was not enhanced in CM GC-A KO mice. Lastly, while the stimulatory effects of Ang II on Ca(2+)-handling were absent in myocytes of mice deficient in TRPC3/TRPC6, the effects of isoproterenol were unchanged. Our data demonstrate a direct myocardial role for ANP/GC-A/cGMP to antagonize the Ca(2+) (i)-dependent hypertrophic growth response to Ang II, but not to beta-adrenergic stimulation. The selectivity of this interaction is determined by PKG I and RGS2-dependent modulation of Ang II/AT(1) signalling. Furthermore, they strengthen published observations in neonatal cardiomyocytes showing that TRPC3/TRPC6 channels are essential for Ang II, but not for beta-adrenergic Ca(2+) (i)-stimulation in adult myocytes.