Studies have shown that Berberine exerts cardio-protective effects in animal models however much less is known regarding its molecular mechanism. Thus the present study was undertaken to elucidate the effect of Berberine on cardiovascular system in terms of signal transduction. To assess and confirm the cardio protective effect of Beberine, rat embryonic heart derived H9c2 cells were cultured under hypoxic condition in serum free DMEM/F-12 medium with and without Berberine treatment. At the end of hypoxic treatment medium was collected and subjected to LDH release assay. Also the effect of Berberine on vascular smooth muscle cells was investigated. HCASMCs and rVSMCs were pre treated with Berberine for 30 min then stimulated with Ang II. Equal amounts of proteins were used for western blot. Activated Erk 1/2 protein was visualized using phospho-specific anti-Erk 1/2 antibody. According to the result of LDH release assay, in Berberine treated groups the amount of LDH released was significantly decreased compared to control group (hypoxia only) after 2hrs of treatment and this protective effect was concentration dependent. In both HCASMCs and rVSMCs Berberine pretreatment inhibited Ang II induced Erk 1/2 activation. These results indicate that Berberine can protect cardiomyocytes in case of hypoxia /reperfusion injury and prevent restenosis in vascular smooth muscle cells. Since MAPKs such as Erk, JNK and p38 are important mediators in hypertrophic signal transduction in vascular smooth muscle cells and previous studies have shown that Berberine treatment inhibited hypertrophy in vivo, it is plausible that protective effect of Berberine in cardiovascular system is mainly due to its inhibitory effect on Erk activation.