Myc is a highly pleiotropic transcription factor that coordinates multiple transcriptional programmes involved in cell replication and differentiation, metabolism and apoptosis. With the development of animal models allowing for switchable ectopic Myc expression in vivo, it has become evident that Myc also controls diverse cell extrinsic processes required for tissue regeneration, in a manner that is tightly tailored to the tissue in which Myc is activated. Since deregulated and elevated Myc expression is a pervasive and causal attribute of most tumours, understanding how tissue-specific responses to Myc are determined at a molecular level is imperative. We have developed an in vivo model permitting determination of the immediate transcriptional and phenotypic consequences of Myc activation across all tissues of an adult mouse. Myc activation elicits an acute proliferative response in some, but not all, organs with a striking correlation between proliferation and the regenerative capacity of individual tissues. Despite such disparities in proliferative response, Myc binds to open, active chromatin in both responsive (liver) and non-responsive (heart) tissues, while a significant transcriptional response to Myc binding is seen only in liver and other responsive tissues. Using the heart as an exemplar of a non-responsive tissue, we show that Myc-driven transcription may be re-engaged in vitro and in vivo by elevating levels of general transcription factors and RNA Polymerase II, leading to a profound proliferative response to Myc in mature cardiomyocytes. Hence, modulation of transcription activity potential is a key determinant of whether an individual tissue is permissive for Myc transcriptional activation. Overall, our data indicate that tissue regenerative capacity is tightly linked to the capacity of that tissue to respond to Myc and that overall tissue Myc responsiveness is governed principally by availability of key components of the core transcriptional machinery, which Myc co-opts to drive its regenerative biological output.