Defining conserved molecular pathways in animal models of successful cardiac regeneration could yield insight into why adult mammals have inadequate cardiac regeneration after injury. Here we describe a cross-species transcriptomic screen to identify evolutionarily conserved pathways in the early events of cardiac regeneration in three species that can regenerate myocardium after a major injury. In this study, we performed RNA-seq on regenerating hearts from three model organisms - axolotl, zebrafish and mouse. Apical resection was performed to amputate ~10 - 20% of the left ventricle in all three model organisms. Following resection, hearts were harvested at 12, 24 and 48 hours post-resection and subjected to RNA-seq. RNA-seq on sham controls (no ventricular amputation) was used as interanal control. This approach revealed upregulation of inflammatory genes in all three organisms during regeneration. Furthermore, upregulation of Complement 5a receptor1 (C5aR1) expression in the regenerating hearts of zebrafish, axolotls and mice was observed. Overall design: Examination of differentially expressed genes in early cardiac regeneration in three model organisms - zebrafish, axolotl and mouse.