Fructose feeding has been shown to induce the cardiac -MHC (myosin heavy chain) expression, and protect the heart from ischemia-reperfusion mediated cell-injury. This study was designed to investigate the mechanism involved in the effect of this sugar on MHC gene expression and cardiac protection. Adult mice were fed with a PTU (6-propyl-2-thiouracil) diet or PTU combined with a fructose-rich diet. PTU treatment made animals hypothyroid and that resulted into total replacement of cardiac -MHC with the -MHC isoform. Addition of fructose into PTU diet led to re-expression of -MHC isoform to a significant level. Similar induction of α-MHC expression was also seen when PTU diet was combined with resveratrol, an agonist of SIRT1 deacetylase. Analysis of heart lysate of these animals indicated that fructose feeding augmented the NAD/NADH ratio and the cardiac SIRT1 levels, thus suggesting a role of SIRT1 in fructose-mediated activation of -MHC isoform. To analyze a direct effect of SIRT1 on MHC isoform expression, we generated transgenic mice expressing SIRT1 in the heart. Treating these transgenic mice with PTU diet did not let disappearance of -MHC, as it did in the non transgenic animals. SIRT1 over expression also activated the -MHC gene promoter in transient transfection assays, thus confirming a role of SIRT1 in the induction of -MHC expression. Fructose feeding also attenuated the MHC isoform shift and blocked the cardiac hypertrophy response associated with pressure overload, which was again associated with the induction of cardiac SIRT1 levels. These results demonstrate that fructose feeding protects the heart by induction of the SIRT1 deacetylase and highlight its role in the induction of α-MHC gene expression.