ObjectiveTo study the dynamic changes of rat donor myocardial cell apoptosis during hypot hermic preservation and the effect of melatonin.MethodsEighty rats were randomly divided into two groups: experimental group with the i solated rat hearts being preserved in 4?℃ St Thomas solution with melatonin ( 0.1?mmol/L ); control group with the isolated rat hearts being preserved in 4?℃ St Thomas solution only. After preservation for 4, 8, 12, 24 and 36?h, a poptotic index was evaluated by the percentage of mycardial cells using TUNEL po sitive staining.ResultsWith the hypothermic preservation time prolonging, more myocardial cell apoptosi s was found (control group, P