Abstract： Background Nitric oxide (NO) is a biologically active molecule which has been reported to protect the heart against ischemia and reperfusion injury in different species.This study aimed to test the hypothesis that nitric oxide may induce the expression of heat shock protein 72 (HSP72) which may protect the heart against ischemia.Methods Rabbits were given intravenous saline or S-nitroso-N-acetyIpenicillamine (SNAP),a nitric oxide donor,or Zaprinast,an inhibitor of cyclic guanosine monophosphate (GMP)-phosphodiesterase,which may increase myocardial cyclic GMP content.Twenty-four hours later,the rabbits were either sampled to measure HSP72,or induced with a 30-minute coronary occlusion followed by a 120-minute reperfusion,and then the infarct size was measured.Meanwhile,chelerythrine (CHE,an inhibitor of protein kinase C) was given intravenously 5 minutes before SNAP injection and the effect on HSP72 expression and infarct size was determined.Results Twenty-four hours after pretreatment,immunoblotting showed HSP72 expression increased in the SNAP group compared with control groups,and this was blocked by CHE.Myocardial infarct size in the SNAP group was smaller than that of the control group ((32.4±5.8)% vs (51.1±4.7)%,P＜0.05).Pretreated with CHE abolished the infarct size-limiting effect of SNAP((46.0±5.1)%).Pretreatment with Zaprinast neither induced HSP72 expression nor reduced infarct size((55.4±5.4)%).Conclusion NO induced HSP72 expression and a delayed protection to the heart via the activities of protein kinase C by a cyclic GM P-independent pathway.