The aim of this study was to examine the individual contribution of specific heat stress proteins in primary rat cardiocytes to any protection observed following lethal heat stress or simulated lethal ischaemia. cDNAs for the inducible heat stress protein 70, for heat stress proteins 90 or 60, or a control plasmid were contransfected with a detectable marker, alkaline phosphatase, into cardiocytes. Survival assays were performed after the lethal stress. Transfection of the inducible heat stress protein 70 was found to increase survival following a lethal heat stress by 2.45-fold (P < 0.01) and against lethal ischaemia by 2.71-fold (P < 0.01). Transfection of heat stress protein 90 improved survival against heat by 2.55-fold (P < 0.05) but failed to have any effect on survival against lethal ischaemia. Transfection of heat stress protein 60 offered no protection against either stress.