Fig. 4. Effect of hypoxic preconditioning (5 min of severe hypoxia) on the loss of cardiac output () during a subsequent 30 min hypoxic exposure (N=7–8 in each group): 5 min of hypoxic-preconditioning (filled squares); 30 min of severe hypoxia (filled circles); and 30 min of severe hypoxia following 5 min of hypoxic preconditioning (open squares). Repeated-measures ANOVA indicated that pre-exposure to 5 min of hypoxia did not affect the rate at which fell when hearts were exposed to 30 min of severe hypoxia. Values are means ± S.E.M.