PW1+/Pax7– skeletal muscle-derived interstitial progenitor cells (PICs) are myogenic in vitro, efficiently contribute to skeletal muscle regeneration in vivo, and are self-renewing in vivo whilst also giving rise to satellite cells (Mitchell et al. 2010). They have previously been identified in the mouse and pig and are bi-potent forming both smooth and skeletal muscle (Mitchell et al. 2010, Lewis et al. 2014). This study characterised murine PICs for stem cell properties of self-renewal, clonogenicity and multipotency. Furthermore, PW1 expression was assessed in cardiac tissue, and in an isolated Sca1+ cardiac stem cell population. Satellite cells and PICs were identified and quantified in hind limb skeletal muscle of 3, 10 and 21 day, and 2 year old mice: there was a decline in abundance of both SC and PICs with age. PICs were isolated by MACS technology from hind limb murine skeletal muscle of 21 day old mice, and their phenotype characterised. Isolated PICs expressed markers of pluripotency; Oct3/4, Sox2 and Nanog, were clonogenic and self- renewing over >60 population doublings in vitro, with a population doubling time of 15.8±2.9 hours. Furthermore, PICs demonstrated multipotency both in vitro and in vivo giving rise to cell types from the 3 germ layers. PW1+ cells were identified and quantified with respect to location in the heart on 3, 10 day, 21 day and 2 year old mice with the majority of cells found within the epicardium. There was rapid decline in abundance during postnatal development. CD45-/Sca-1+ CSCs were isolated from 6 week old mice via MACS technology and assessed for PW1 expression (83%). In summary, this study showed PICs have broad developmental plasticity both in vitro and in vivo, and can be propagated and maintained in a primitive state in culture. Furthermore, PW1 also marks a stem cell population within the heart. These data opens new avenues for solid tissue engineering and regeneration utilising a single multi-potent stem cell type, isolated from an easily accessible source such as skeletal muscle.