Background: Gq protein-coupled receptor (GPCR) signaling pathway, which includes diacylglycerol (DAG) and protein kinase C (PKC), plays a critical role in cardiac hypertrophy. DAG kinase (DGK) catalyzes DAG phosphorylation and controls cellular DAG levels, thus acting as a regulator of GPCR signaling. It has been reported that DGK acts specifically on DAG produced by inositol cycling. In this study, we examined whether DGK prevents cardiac hypertrophy and progression to heart failure under chronic pressure-overload. Methods and Results: We generated transgenic mice with cardiac-specific overexpression of DGK (DGK-TG) using an -myosin heavy chain promoter. There were no differences in cardiac morphology and function between wild-type (WT) and DGK-TG mice at basal condition. Either continuous phenylephrine infusion or thoracic transverse aortic constriction (TAC) was performed in WT and DGK-TG mice. Increases in heart weight after phenylephrine infusion and TAC were abolished in DGK-TG mice compared to WT mice. Cardiac dysfunction after TAC was prevented in DGK-TG mice, and survival rate after TAC was higher in DGK-TG mice than in WT mice. Phenylephrine- and TAC-induced DAG accumulation, translocation of PKC isoforms and induction of fetal genes were blocked in DGK-TG mouse hearts. Up-regulation of transient receptor potential channel (TRPC) 6 expression after TAC was attenuated in DGK-TG mice. Conclusion: These results demonstrate the first evidence that DGK restores cardiac dysfunction and improves survival under chronic pressure overload by controlling cellular DAG levels and TRPC 6 expression. DGK may be a novel therapeutic target to prevent cardiac hypertrophy and progression to heart failure.