The adult mammalian heart has limited capacity for regeneration following injury, whereas the neonatal heart can readily regenerate within a short period after birth. Neonatal heart regeneration is orchestrated by multiple cell types intrinsic to the heart, as well as immune cells that infiltrate the heart after injury. To elucidate the transcriptional responses of the different cellular components of the mouse heart following injury, we perform single-cell RNA sequencing on neonatal hearts at various time points following myocardial infarction and couple the results with bulk tissue RNA-sequencing data collected at the same time points. Concomitant single-cell ATAC sequencing exposes underlying dynamics of open chromatin landscapes and regenerative gene regulatory networks of diverse cardiac cell types and reveals extracellular mediators of cardiomyocyte proliferation, angiogenesis, and fibroblast activation. Together, our data provide a transcriptional basis for neonatal heart regeneration at single-cell resolution and suggest strategies for enhancing cardiac function after injury.