The objective is to determine if Hsp70 is involved in the mechanism by which serum from burn rats induces apoptosis of cardiomyocytes. Cardiomyocytes in primary culture were assigned to the following groups: normal controls, normal rat serum, burn serum, burn serum plus empty vector control, and burn serum plus Hsp70 transfection. Each group, except normal controls, was cultured with the corresponding serum for 2 hours. The empty vector controls and the Hsp70 groups were transfected, respectively, with the empty vector or pcDNA3.1-Hsp70 recombinant plasmid 36 hours previously. Hsp70 protein levels were assessed by Western blot. Apoptotic cells were counted after Hoechst 33258 staining. Apoptosis of cardiomyocytes was also detected by the presence of "ladder" bands in agarose gels following electrophoresis of extracted DNA. Activation of caspase-3, -8, and -9 and Bid cleavage were assessed by Western blot. Hsp70 overexpression inhibited burn serum-induced apoptosis of cardiomyocytes; and burn serum-induced activation of caspases-3, -8, and -9; and Bid cleavage into tBid. Hsp70 inhibits burn serum-induced apoptosis by interfering with death receptor and mitochondrial pathways.