The ability of heat stress to improve the survival of ischemic-reperfused skeletal muscle in vivo was investigated. Ischemia-reperfusion was applied using the rat hindlimb tourniquet model. The viability of ischemic-reperfused muscle (11 +/- 1%) was increased by prior mild heat stress (86 +/- 2%). To investigate whether heat shock protein 70 (Hsp 70) expression in the muscle of the heated limb was responsible for this protection, the survival of Hsp 70-expressing transduced myoblasts and myocytes was measured after exposure to mediators of ischemia-reperfusion injury. Survival was improved in Hsp 70-positive myoblasts but not in myocytes, suggesting that the mechanism of protection conferred by heat stress in vivo cannot be explained by the expression of Hsp 70 in myocytes and may involve a more complex mechanism. In conclusion, prior heat stress is effective in protecting mature skeletal muscle in vivo against necrosis after ischemia-reperfusion and has potential for use in microsurgical procedures requiring tourniquet applications.