The aim of this study was to investigate (1) whether Rhodobryum roseum, a traditional Chinese medicine used to treat cardiac disease, can protect myocardium damage due to isoproterenol-induced injury, (2) whether the cardioprotective effect of the R. roseum extract is related to its antioxidant activity, and (3) to identify the active components of R. roseum using the oxidant-mediated injury in cardiomyocytes. R. roseum was extracted with 95% EtOH (RE-95), 50% EtOH (RE-50) and water (Re-H2O) and the rats were treated orally for 11 days at doses of 250 mg and 63 mg/kg respectively after cardiac necrosis was induced by administering ISO subcutaneously at a dose of 85 mg/kg body weight. Levels of marker enzymes (LDH, GOT and CK) were assessed in serum whilst the antioxidant parameters, superoxide dismutase (SOD), and malondialdehde (MDA) were assayed in heart homogenate. Significant myocardial necrosis, depletion of endogenous antioxidants and an increase in serum levels of marker enzymes was observed in ISO-treated animals when compared with the normal animals. The RE-50 elicited a significant cardioprotective effect by lowering the levels of serum marker enzymes, lipid peroxidation (MDA). To extend this work, we sought to investigate the antioxidant effects of the components of R. roseum, using the neonatal rat cardiomyocytes model of H2O2-induced oxidant injury. Among the four major components, piperine and methyl piperate significantly reduced the medium level of CK and LDH at a variety of dosages. Moreover, piperine and methyl piperate significantly attenuated 2',7'-dichlorofluorescein (DCF) fluorescence by 63.9% and 52.6%, respectively. The present findings demonstrate that the cardioprotective effects of extracted R. roseum in ISO-induced oxidative damage may be due to an augmentation of the endogenous antioxidants and inhibition of lipid peroxidation of the membranes. Moreover, its components piperine and methyl piperate exert significant protectective effects on cardiac myocytes.