Sixty-nine groups of nine-teen strains mice were used. (A) Mice in groups I–XIX underwent acute myocardial infarction (MI) consisting of 30-min coronary occlusion (O) and followed by 24 h of reperfusion (R). (B) On day 1, mice in the early PC sham (EPC sham) group XXIX were subjected to 60-min open chest 10 min prior to 30-min O and followed by 24 h of R. Mice in the early preconditioned (PC, EPC) groups XX–XXV and XXVII–XXX underwent a sequence of six cycles of 4-min coronary O/4-min R cycles 10 min prior to 30-min O and followed by 24 h of R. (C) On day 1, mice in the late PC sham (LPC sham) groups XXXIII and XLII were subjected to 60-min open chest and underwent 30-min O 24 h later on day 2. Mice in the late PC (LPC) groups XXXI–XXXII, XXXIV–XL and XLIII were preconditioned with six 4-min O/4-min R cycles and underwent 30-min O 24 h later on day 2. (D) Mice in groups XLIV–XLVIII underwent O times ranging from 10–60-min followed by 24 h R. (E) Female mice in groups XLIX–LV underwent MI consisting of 30-min O followed by 24 h R either with or without EPC or LPC stimulus. (F) Mice, ranging in ages from 6–101 wk, in groups LVI–LXIII underwent MI consisting of 30-min O followed by either 4 or 24 h R. (G) ICR mice in groups LXIV–LXIX underwent MI consisting of 30-min O followed by 24 h R, and were compared based on body core temperature and pH differences during surgery. On day 2 or 3, hearts from all groups (I–LXIX) were harvested and subjected to postmortem tissue analysis including triphenyltetrazolium chloride, Phthalo blue dye staining to determine infarct size.