Pathologic hypertrophy of the heart is regulated through membrane-bound receptors and intracellular signaling pathways that function, in part, by altering Ca²⁺ handling and Ca²⁺-dependent signaling effectors. Transient receptor potential canonical (TRPC) channels are important mediators of Ca²⁺-dependent signal transduction that can sense stretch or activation of membrane-bound receptors. Here we generated cardiac-specific transgenic mice that express dominant-negative (dn) TRPC3, dnTRPC6, or dnTRPC4 toward blocking the activity of the TRPC3/6/7 or TRPC1/4/5 subfamily of channels in the heart. Remarkably, all three dn transgenic strategies attenuated the cardiac hypertrophic response following either neuroendocrine agonist infusion or pressure-overload stimulation. dnTRPC transgenic mice also were partially protected from loss of cardiac functional performance following long-term pressure-overload stimulation. Importantly, adult myocytes isolated from hypertrophic WT hearts showed a unique Ca²⁺ influx activity under store-depleted conditions that was not observed in myocytes from hypertrophied dnTRPC3, dnTRPC6, or dnTRPC4 hearts. Moreover, dnTRPC4 inhibited the activity of the TRPC3/6/7 subfamily in the heart, suggesting that these two subfamilies function in coordinated complexes. Mechanistically, inhibition of TRPC channels in transgenic mice or in cultured neonatal myocytes significantly reduced activity in the calcineurin–nuclear factor of activated T cells (NFAT), a known Ca²⁺-dependent hypertrophy-inducing pathway. Thus, TRPC channels are necessary mediators of pathologic cardiac hypertrophy, in part through a calcineurin–NFAT signaling pathway.