Metabolic correlates of hibernator cardioprotective phenotype. We used mass spectrometry–based metabolomics to quantify ischemia–reperfusion injury induced changes in targeted metabolites between hibernating arctic ground squirrels (HIB AGS) and rats. Accumulation of toxic intermediates of lipid metabolism, acylcarnitine (C4DC acylcarnitine; A) and ceramide species (C18-ceramide and d18:1/C18-ceramide; B, C), was found in left ventricular myocardial tissue homogenates from rats compared to arctic ground squirrels, at both the 3-h (R3h) and 24-h (R24h) reperfusion time points, sham surgery (S) is shown for comparison (*P < 0.05, ANOVA with Tukey post hoc correction). Data are presented as mean ± SD, N = 6/group.