Myocardial infarct size depicted as a percentage of left ventricular area at risk in rabbits receiving 0.9% saline (control, CON) or 1, 3, or 5 cycles of 70% helium-30% oxygen administered for 5 min interspersed with 5 min of an air-oxygen mixture (fraction of inspired oxygen concentration = 0.30; panel A, top). Infarct sizes in rabbits receiving the selective glycogen synthase kinase inhibitor SB 216763 (SB21, 0.2 or 0.6 mg/kg) and the combination of one preconditioning cycle of helium and 0.2 mg/kg SB21 in the absence or presence of the mitochondrial permeability transition pore opener atractyloside (ATR; 5 mg/kg) are depicted in panel B (middle). Infarct sizes in rabbits receiving the selective p53 inhibitor pifithrin-α (PIF, 1.5 or 3.0 mg/kg) and the combination of one preconditioning cycle of helium and 1.5 mg/kg PIF in the absence of presence of ATR (5 mg/kg) are depicted in panel C (bottom). Each point represents a single experiment. All data are mean ± sd *Significantly (P < 0.05) different from CON; †Significantly (P < 0.05) different from one cycle of helium pretreatment.