Apoptotic myocyte cell death, diastolic dysfunction and progressive deterioration in LV pump function, characterize the clinical course of diabetic cardiomyopathy. A key question concerns the mechanism(s) by which hyperglycemia (HG)-transmits danger signals in cardiac muscle cells (CMC). The growth factor adapter protein, p66ShcA is a genetic determinant of longevity, which controls mitochondrial metabolism and cellular responses to oxidative stress. Here, we demonstrate interventions that attenuate or prevent HG-induced phosphorylation at critical position 36 Ser residue (phospho-Ser-36), inhibit the redox function of p66ShcA and promote the survival phenotype. Adult rat ventricular myocytes (ARVM) obtained by enzymatic dissociation were transduced with mutant36 p66ShcA (mu-36) dominant negative expression vector and plated in serum free media (SFM) containing 5 mM or 25 mM glucose. At HG, ARVM exhibit marked increase in reactive oxygen species (ROS) production, upregulation of phospho-Ser-36, collapse of mitochondrial transmembrane potential m) and increased formation of p66ShcA/cytochrome c complexes. These indices of oxidative stress were accompanied by 40% increase in apoptosis and upregulation of cleaved caspase 3 and the apoptosis related proteins p53 and Bax. To test if p66ShcA functions as a redox sensitive molecular switch in vivo, we examined hearts of male Akita diabtic nonobese (C57BL/6J) mice. Immunoblot analysis detected upregulation of phospho-Ser-36, translocation of p66ShcA to mitochondria and formation of p66ShcA/cytochrome c complexes. Conversely, correction of HG by adenoassociated viral delivery of leptin (rAAV-Lep) reversed these alterations. We conclude p66ShcA is a molecular switch whose redox function is turned on by phospho-Ser-36 and turned off by interventions that prevent this modification.