Sirtuin 1 (SirT1) is the largest of the seven members of the sirtuin family of class III nicotinamide adenine dinucleotide (NAD + )-dependent protein deacetylases, whose activation is beneficial for metabolic, neurodegenerative, inflammatory and neoplastic diseases, and augments life span in model organisms ( Finkel et al., 2009 ; Lavu et al., 2008 ). In vitro studies show that SirT1 protects genome integrity and is involved in circadian physiological rhythms ( Asher et al., 2008 ; Nakahata et al., 2008 ; Oberdoerffer et al., 2008 ). In the last few years, a fundamental role for SirT1 in the metabolism and differentiation of skeletal muscle cells has been uncovered ( Fulco et al., 2003 ), and the use of specific transgenic or knockout SirT1 mouse models implicates it in the protection of heart muscle from oxidative and hypertrophic stresses ( Alcendor et al., 2007 ). In this Perspective, we review the recent exciting findings that have established a key role for the ’longevity’ protein SirT1 in skeletal and heart muscle physiology and disease. Furthermore, given the multiple biological functions of SirT1, we discuss the unique opportunities that SirT1 mouse models can offer to improve our integrated understanding of the metabolism, as well as the regeneration and aging-associated changes in the circadian function, of skeletal and heart muscle.