Myocardial infarct size in non-preconditioned (naïve) hearts from mice ranging in ages from 6–101 wk V, IX, XIV, XIX and LIII–LIX underwent MI consisting of 30-min O, followed by 24 h R (Fig. 1 F). Infarct is expressed as percentage of region at risk of infarction. Individual mice (○) and Mean ± SEM (●), for respective groups (n, number of mice).