POSTN and myocardial infarction: The cardiac extracellular matrix (ECM) composition undergoes considerable changes throughout in utero development, when CMs are most proliferative, to postnatal maturation, when CMs exhibit limited proliferative capacity.13 47 48 Furthermore, the cardiac ECM undergoes distinct changes post-MI, with inflammation, proteolysis and fibrotic scar formation significantly altering infarct and BZ ECM expression.49 50 An early study identified the ECM protein periostin as an inducer of proliferation and CM repair.51