AimsCardiac fibrosis contributes to the transition from compensated ventricular hypertrophy to heart failure, which can be promoted by connective tissue growth factor (CTGF). Trimetazidine (TMZ), an anti-angina drug, also has benefits in non-ischaemic heart disease. We wondered whether TMZ has an effect on cardiac fibrosis from pressure overload by downregulating CTGF. Methods and results: Male Sprague-Dawley rats underwent transverse aortic constriction (TAC) or sham operation and then after 20 weeks were assigned to receive TMZ or saline for another 5 weeks. TMZ significantly inhibited collagen accumulation, CTGF expression, and reactive oxygen species (ROS) production induced by TAC. Furthermore, the effects of TMZ on ROS, the upstream signal of CTGF synthesis signal transduction, were evaluated in cardiac fibroblasts. The result showed that the ROS level was reduced by TMZ on stimulation with angiotensin II. Additionally, the NADPH oxidase activity was ameliorated with TMZ by the regulation of translocation of its subunit Rac1. Conclusion: TMZ effectively inhibits myocardial fibrosis, perhaps through the NADPH oxidase-ROS-CTGF signalling pathway. Our findings may be used to provide new clues for the potential function of TMZ in pressure overload-induced myocardial fibrosis. © The Author 2010.