The inability of the adult mammalian heart to regenerate following injury represents a major barrier in cardiovascular medicine. In contrast, the neonatal mammalian heart retains a transient capacity for regeneration, which is lost shortly after birth. Defining the molecular mechanisms that govern cardiac regenerative capacity in the neonate remains a central goal in regenerative biology. Here, we construct a transcriptional atlas of multiple cardiac cell populations in the neonatal and adult heart, which enables comparative analyses of the response to myocardial infarction for the first time. Our transcriptomic analyses identify a neonatal proliferative network, which is silenced in adult cardiomyocytes and associated with chromatin compaction around cell cycle genes during post-natal maturation. Complimentary high-throughput screening studies in human cardiac organoids revealed that a switch in metabolism from glycolysis to fatty acid oxidation drives post-natal cardiomyocyte cell cycle arrest via repression of b-catenin and Yap-dependent signaling. In ongoing studies, we are employing a number of strategies to overcome the proliferative barrier imposed by cardiomyocyte metabolism. These findings uncover key transcriptional circuits under the control of cardiomyocyte metabolism, which could be harnessed for cardiac regeneration following injury.