Angiotensin (Ang) II participates in the pathogenesis of heart failure through induction of cardiac hypertrophy. Ang II-induced hypertrophic growth of cardiomyocytes is mediated by nuclear factor of activated T cells (NFAT), a Ca(2+)-responsive transcriptional factor. It is believed that phospholipase C (PLC)-mediated production of inositol-1,4,5-trisphosphate (IP(3)) is responsible for Ca(2+) increase that is necessary for NFAT activation. However, we demonstrate that PLC-mediated production of diacylglycerol (DAG) but not IP(3) is essential for Ang II-induced NFAT activation in rat cardiac myocytes. NFAT activation and hypertrophic responses by Ang II stimulation required the enhanced frequency of Ca(2+) oscillation triggered by membrane depolarization through activation of DAG-sensitive TRPC channels, which leads to activation of L-type Ca(2+) channel. Patch clamp recordings from single myocytes revealed that Ang II activated DAG-sensitive TRPC-like currents. Among DAG-activating TRPC channels (TRPC3, TRPC6, and TRPC7), the activities of TRPC3 and TRPC6 channels correlated with Ang II-induced NFAT activation and hypertrophic responses. These data suggest that DAG-induced Ca(2+) signaling pathway through TRPC3 and TRPC6 is essential for Ang II-induced NFAT activation and cardiac hypertrophy.