While lower vertebrates can repair their adult hearts after a heart attack, mammals — including humans — cannot. The ability to regenerate dead muscle tissue in mammalian hearts disappears just a few days after birth because the heart muscle cells, called cardiomyocytes, exit the cell cycle. In 2020, researchers reported that surgery to remove the left ventricle apex of the heart of pigs, one day after birth, somehow extended the replication ability of heart muscle cells. To better understand the underlying gene expression changes in this extended regeneration window, researchers now report nuclear RNA-sequencing of heart muscle cells, using this porcine model. From such knowledge, and much further research yet to come, clinicians may potentially learn how to regenerate adult heart cardiomyocytes after a heart attack.