The protective effect of aspirin during exposure to heat stress in broiler chickens was investigated.We assayed the pathological damage,expression and distribution of Hsp90 protein and the hsp90 mRNA expression in chicken heart tissues after oral administration of aspirin following exposure to high temperature for varying times.Heat stress induced increases in plasma aspartate aminotransferase,creatine kinase and lactate dehydrogenase activities,and caused severe heart damage,characterized by granular and vacuolar degeneration,nuclear shrinkage and even myocardium fragmentation in cardiac muscle fibers.After aspirin administration,myocardial cells showed fewer pathological lesions compared with broilers only treated by heat.A high positive Hsp90 signal was always detected in the nuclei of myocardial cells administrated with aspirin,while in myocardial cells treated with heat alone,Hsp90 in the nuclei decreased,along with a decrease in the cytoplasm.Aspirin could induce rapid and significant synthesis of Hsp90 before and at the initial phase of heat stress,and significant expression of hsp90 mRNA was stimulated throughout the whole process of experiment,compared with cells exposed to heat stress only.Thus,the specific pre-induction of Hsp90 in cardiovascular tissue was useful preparation for resisting heat-stress damage,characterized by stable damage-relative enzymes and fewer pathologic changes.