The eNOS expression in the cardiac hypertrophy group was inhibited, but tanshinone IIA can significantly improve the phosphorylation of p-eNOS (Ser1177) in the myocardial tissue of rats to enhance the activity of eNOS and can also down-regulate the Nox4 expression to reduce the vitality of NADPH, which ultimately protects against cardiac hypertrophy in SHRs. The gene discussed is NOX4; the disease is cardiac hypertrophy.