Introduction: The abundantly expressed small molecular weight proteins, CRYAB and HSPB2, have been implicated in cardioprotection ex vivo. However, the biological roles of CRYAB/HSPB2 co-expression for either ischemic preconditioning and/or protection in situ remain poorly defined. Methods: Wild type (WT) and age-matched (~5-9 months) CRYAB/HSPB2 double knockout (DKO) mice were subjected either to 30 minute coronary occlusion and 24 hours of reperfusion in situ, or preconditioned with 4-minute coronary occlusion/4-minute reperfusion x 6, before similar ischemic challenge (ischemic PC). Additionally, WT and DKO were subjected to 30 minutes of global ischemia in isolated hearts ex vivo. All experimental groups were assessed for area-at-risk and infarct size. Mitochondrial respiration was analyzed in isolated permeabilized cardiac skinned fibers. Results: DKO modestly altered HSP expression. Surprisingly, infarct size in situ was reduced by 35% in hearts of DKO compared with WT mice (38.8±17.9 vs. 59.8±10.6% area-at-risk, p<0.05). In DKO, ischemic PC was additive to its 'infarct-sparing' phenotype. Similarly, infarct size after ischemia and reperfusion ex vivo was decreased and the production of superoxide and creatine kinase release was decreased in DKO compared with WT (p<0.05). In permeabilized fibers, ADP-stimulated respiration rates were modestly reduced and calcium-dependent ATP synthesis was abrogated in DKO compared with WT. Conclusion: Contrary to expectation, our findings demonstrate that CRYAB and HSPB2 deficiency induces profound adaptations that are related to (a) a reduction in calcium-dependent metabolism/respiration, including ATP production, and (b) decreased superoxide production during reperfusion. We discuss the implications of these disparate results in the context of phenotypic responses reported for CRYAB/HSPB2 deficient mice to different ischemic challenges.