Background— Although disruption of guanylyl cyclase (GC) A, a natriuretic peptide receptor, induces cardiac hypertrophy and fibrosis, the molecular mechanism underlying these effects are not well understood. In this study, we examined the role of calcineurin, a calcium-dependent phosphatase, in cardiac remodeling in GCA-knockout (GCA-KO) mice. Methods and Results— At 14 weeks of age, calcineurin activity, nuclear translocation of nuclear factor of activated T cells c3 (NFATc3), and modulatory calcineurin-interacting protein 1 (MCIP1) gene expressions were increased in the hearts of GCA-KO mice compared with wild-type (WT) mice. Blockade of calcineurin activation by FK506 (6 mg/kg body weight administered subcutaneously once a day from 10 to 14 weeks of age) significantly decreased the heart-to-body weight ratio, cardiomyocyte size, and collagen volume fraction in GCA-KO mice, whereas FK506 did not affect these parameters in WT mice. Overexpression of atrial and brain natriuretic peptides, collagen, and fibronectin mRNAs in GCA-KO mice was also attenuated by FK506. Electrophoretic mobility shift assays demonstrated that GATA4 DNA-binding activity was increased in GCA-KO mice, and this increase was inhibited by calcineurin blockade. In neonatal cultured cardiac myocytes, inhibition of GCA by HS142-1 (100 μg/mL) increased basal and phenylephrine (10 − 6 mol/L)-stimulated calcineurin activity, nuclear translocation of NFATc3, and MCIP1 mRNA expression. In contrast, activation of GCA by atrial natriuretic peptide (10 − 6 mol/L) inhibited phenylephrine (10 − 6 mol/L)-stimulated nuclear translocation of NFATc3. Conclusions— These results suggest that activation of cardiac GCA by locally secreted natriuretic peptides protects the heart from excessive cardiac remodeling by inhibiting the calcineurin-NFAT pathway.