||Cardiovascular disease is one of the leading causes of death in many countries. Danshen-Gegen (DG) decoction is a traditional Chinese herbal formula, which has been reported to be effective for the treatment of cardiovascular diseases including myocardial infarction. Isoproterenol (ISO) treatment caused acute and chronic myocardial injury in rats, as evidenced by increases in plasma enzyme activities and/or histopathological changes in heart ventricular tissues. The ISO-induced myocardial injury was associated with the impairment in mitochondrial glutathione antioxidant status, as assessed by reduced glutathione (GSH) level and activities of glutathione-related antioxidant enzymes. The impaired mitochondrial antioxidant status was paralleled by an increased extent of lipid peroxidation. The ISO challenge impaired mitochondrial glutathione redox status in rat hearts, as assessed by the GSH/oxidized glutathione (GSSG) ratio. The ISO-induced acute myocardial injury was associated with increases in mitochondrial Ca2+ loading and cytochrome c release, which are probably related to mitochondrial permeability transition (MPT). Paradoxically, decreases in mitochondrial Ca2+ loading and cytochrome c release were observed in chronic myocardial injury induced by ISO. DG post-treatment protected against ISO-induced acute or chronic myocardial injury in rats, as evidenced by the inhibition of plasma enzyme activities or improvement of histological parameters. The cardioprotection afforded by DG post-treatment was associated with a reversal of altered mitochondrial glutathione antioxidant parameters and a reduction in the extent of mitochondrial lipid peroxidation in ISO-challenged rats. DG post-treatment also reduced the extents of mitochondrial Ca2+ loading and cytochrome c release in the rats acutely challenged with ISO. The downstream targets of RISK pathway include PKCε and mKATP. The cardioprotection against ISO-induced acute myocardial injury afforded by DG post-treatment was abolished by PKCε or mKATP inhibition. The abolition of cardioprotection was associated with increased extent of mitochondrial GSH depletion and lipid peroxidation in ISO-challenged rat hearts. On the other hand, Akt inhibition was able to abrogate the cardioprotective effect of DG post-treatment on ISO-induced chronic myocardial injury in rats. The blockade of SAFE pathway by STAT-3 inhibition completely abrogated the cardioprotection against ISO-induced acute myocardial injury in rats. The abolition of cardioprotection was also associated with an increased extent of mitochondrial GSH depletion and lipid peroxidation. In conclusion, DG myocardial postconditioning is likely afforded by the enhancement of mitochondrial glutathione redox status and inhibition of MPT via the activation of RISK and SAFE pathways under oxidative stress condition. Our findings suggest the therapeutic application of DG extract for myocardial postconditioning in patients suffering from myocardial infarction.