Objective— ATP-binding cassette transporter subfamily G member 2 (ABCG2), expressed in microvascular endothelial cells in the heart, has been suggested to regulate several tissue defense mechanisms. This study was performed to elucidate its role in pressure overload–induced cardiac hypertrophy. Methods and Results— Pressure overload was induced in 8- to 12-week-old wild-type and Abcg2 −/− mice by transverse aortic constriction (TAC). Abcg2 −/− mice showed exaggerated cardiac hypertrophy and ventricular remodeling after TAC compared with wild-type mice. In the early phase after TAC, functional impairment in angiogenesis and antioxidant response in myocardium was found in Abcg2 −/− mice. In vitro experiments demonstrated that ABCG2 regulates transport of glutathione, an important endogenous antioxidant, from microvascular endothelial cells. Besides, glutathione transported from microvascular endothelial cells in ABCG2-dependent manner ameliorated oxidative stress–induced cardiomyocyte hypertrophy. In vivo, glutathione levels in plasma and the heart were increased in wild-type mice but not in Abcg2 −/− mice after TAC. Treatment with the superoxide dismutase mimetic ameliorated cardiac hypertrophy in Abcg2 −/− mice after TAC to the same extent as that in wild-type mice, although cardiac dysfunction with impaired angiogenesis was observed in Abcg2 −/− mice. Conclusion— ABCG2 protects against pressure overload–induced cardiac hypertrophy and heart failure by promoting angiogenesis and antioxidant response.