“…In mice, the majority of cardiomyocytes are determined within the first week of postnatal life, followed by two waves of DNA synthesis leading to binucleation and increased ploidy, a measure of genome size [ 4 ]. A small fraction of cardiomyocytes re-enter the cell cycle in response to injury [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]; however, cytokinesis is incomplete after cardiomyocytes re-enter the cell cycle, leading to further polyploidization and limited generation of new cardiomyocytes [ 14 ]. Human cardiomyocyte turnover is ~0.04% in the first year of life and ~0.01% per year in adulthood based on nuclear bomb test-derived radioisotope decay estimates [ 4 , 5 , 15 , 16 ].…”