Abstract: Objective To investigate the role of HO-1 in protection rat hearts from anoxia/reoxygenation induced injury and its underlying mechanism. Methods LVEDP, LVDP and ±dP/dtmax were analyzed by the Langendorff method in isolated rat hearts. Lactate dehydrogenase (LDH), infarct area, COHb and 6-keto-PGF1α were further determined in the experiment. Results After intraperitoneal injection of HO-1 inducer hemin, CO concentration in rat blood enhanced (P<0.01 vs control group). Pretreatment of hemin prevented the increase in LVEDP and decrease in LVDP, ±dp/dtmax during the anoxia and reoxygenation period in hearts. Hemin had no effect on changes of coronary flow, but it really inhibited the release of LDH from anoxia/reoxygenation hearts. Hemin also reduced the infarct area in anoxia heart after 2h reoxygenation (P<0.01). CO concentration in rat blood reduced after intraperitoneal injection of HO-1 inhibitor ZnPP (P<0.01 vs control group). ZnPP aggravated the decrease in LVDP and ±dp/dtmax. Compared with anoxia/reoxygenation heart, pretreatment of ZnPP enhanced the LDH release and enlarged the infarct area (P<0.05). cyclooxygenase-2 (COX-2) inhibitor celecoxib partly abolished the protection effect of hemin on LVEDP, LVDP and ±dp/dtmax. Pretreatment of celecoxib could also cancel the inhibition of LDH release and reduction of infarct area caused by hemin (P<0.05). Conclusions The results shown that HO-1 inducer hemin could protect heart from anoxia/reoxygenation induced injury. The activation of COX-2 might be also involved in the cardiac protection of HO/CO.