Adult mammalian hearts are incapable of regenerating lost cardiomyocytes (CMs) after injury, replacing them instead with akinetic scar tissue that negatively impacts cardiac function. The adult human heart is notorious for its limited regenerative potential; evidence from multiple studies suggests that the CM turnover rate may be as little as 1% or less per year. For this reason, decades of research efforts have focused on stimulating CM proliferation following trauma. To date, delivery of stem and progenitor cells to the injured mammalian myocardium has had limited success in improving cardiac function. A promising alternative approach involves activating endogenous regeneration programs that are conserved through evolutionary history, present in vertebrates such as the zebrafish. The zebrafish heart can fully regenerate following partial resection of the adult cardiac ventricle, or genetic ablation of CMs in adult or embryonic hearts. Virtually all regenerated myocardium derives from pre-existing CMs that sequentially de-differentiate and proliferate. However, a mechanistic understanding of how this process occurs has yet to be described in detail, and specific molecular markers for CMs in the early stages of de-differentiation and cell-cycle re-entry are undefined. Following chemical-genetic ablation of ventricular CMs in embryonic zebrafish hearts, it has previously been demonstrated that atrial CMs de-differentiate and proliferate to re-populate ventricular myocardium (Zhang, R. et al, Nature, 2013). Importantly, a transient population of atrium-derived de-differentiated CMs was identified that had terminated expression of the atrium-specific marker amhc, but had not yet adopted a ventricular CM fate, as measured by expression of the ventricle-specific marker vmhc. Here I present the embryonic zebrafish heart as a model to study the process of CM de-differentiation in the context of myocardial regeneration. By combining cell lineage tracing techniques with a temporally-sensitive reporter for heart chamber-specific gene expression, I present a strategy for the isolation of de-differentiated CMs for further transcriptional analysis.