Abstract： To study the alterations of heme oxygenase-1 mRNA in neonatal rat cardiomyocytes (NRCMs) induced by lipopolysaccharide (LPS) and the role of heme oxygenase-1 (HO-1) in the LPS induced disorders of myocardium function, 10 (L, 6 h), 30 (M, 6 h), 50 μg/ml (H, 6 h) LPS and 10 μg/ml LPS +10 μmol/ml Zn-protoporphyrin-Ⅸ (ZnPPⅨ; L+I, 6 h) and 10 μmol/ml ZnPPⅨ alone (I, 6 h) were added to the medium for a 6-hour culture of NRCMs, and 10 μg/ml LPS for 9 h (L, 9 h) and 18 h (L, 18 h) cultures. LDH release and MDA contents of the cells were measured. When NRCMs were collected, Trypan blue stain method was used to examine the mortality (the rate of Trypan blue uptake) of NRCMs. HO-1 mRNA expression was examined by Northern blot. The results showed that HO-1 mRNA expression of NRCMs increased gradually along with the increase of LPS concentration below the level of 30 μg/ml. When the final concentrations of LPS were 10 and 30 μg/ml, the HO-1 mRNA expression of NRCMs increased by 81.2% and 126.3% respectively compared with control. When the final concentration of LPS was 50 μg/ml, the HO-1 mRNA expression decreased to the level of 10 μg/ml group.　 When the 　final 　　concentration 　was 10 μg/ml,　 the HO-1 mRNA　 expression 　increased 　gradually along with the culture time.　 After a 9- or 18-hour culture, the HO-1 mRNA expression of NRCMs increased by 93.6% and 105.8% respectively compared with control.Only when NRCMs had been cultured with 30, 50 μg/ml LPS and 10 μg/ml LPS +10 μmol/ml ZnPPⅨ for 6 h and 10 μg/ml LPS for 18 h, the rate of Trypan blue stain uptake, MDA contents and LDH release significantly increased. With 10 μg/ml LPS alone and 10 μmol/ml ZnPPⅨ alone for 6 h, the above parameters were not significantly increased (P>0.05). The results demonstrate that LPS induces HO-1 mRNA expression of NRCMs dose- and time-dependently to some extent. The inducible HO can protect NRCMs from injury and thus play an important role in pathogenesis of myocardium under LPS.