Objective To evaluate the role of mammalian target of rapamycin (mTOR ) in reduction of oxygen-glucose deprivation and restoration (OGD/R )-induced injury to isolated cardiomyocytes by hypoxic preconditioning (HPC) in neonatal rats .Methods Primary cardiomyocytes were obtained from neonatal Sprague-Dawley rats (1-3 days after birth ) ,and seeded in 96-well plates at the density of 1 × 105 cells/ml (200μl/well ) . The cells were randomly divided into 6 groups ( n=6 each ) using a random number table:control group (group C) ,rapamycin group (group R) ,group OGD/R ,rapamycin+OGD/R group (group R+OGD/R);group HPC+OGD/R ,and rapamycin+HPC+OGD/R group (group R+HPC+OGD/R) .Rapamycin (final concentration 20 nmol/L) was added to the culture media and the cells were then incubated for 1 h in group R .In R+OGD/R group ,rapamycin (final concentration 20 nmol/L ) was added to the culture media ,the cells were then incubated for 1 h ,and then OGD/R was performed .In HPC+OGD/R group ,OGD/R was performed immediately after HPC was completed .In R+HPC+OGD/R group ,rapamycin (final concentration 20 nmol/L) was added to the culture media ,the cells were then incubated for 1 h , and then HPC and OGD/R were performed . All the cells were subjected to OGD for 2 h followed by restoration of O2-glucose supply for 3 h to induce OGD/R .HPC was induced by 3 cycles of 10 min hypoxia followed by 30 min reoxygenation .The cell viability (using MTT assay ) and lactic dehydrogenase (LDH) activity in the culture medium were determined .Results Compared with group C ,the cell viability was significantly decreased , and LDH activities in the culture medium were increased in OGD/R , R+OGD/R ,HPC+OGD/R and R+ HPC+OGD/R groups ( P<0.05 ) ,while no significant change was found in the cell viability and LDH activities in R group ( P>0.05) .The cell viability was significantly higher ,and LDH activity in the culture medium were lower in HPC+OGD/R group than in OGD/R group ,and in R+HPC+OGD/R group than in HPC + OGD/R group ( P< 0.05 ) .Conclusion mTOR is involved in HPC-induced attenuation of OGD/R injury to isolated cardiomyocytes in neonatal rats .