Youth is wasted on the young

Amphibians and zebrafish are able to regenerate lost myocardial tissue without loss of cardiac function; whereas mammals, in response to myocardial injury, develop scar and lose cardiac function. This dichotomy of response has been thought to be due to the fact that adult mammalian cardiac myocytes are multinucleated and have limited proliferative capacity. Neonatal mammalian cardiac myocytes do have a limited capacity to proliferate. What has been unknown is whether this limited proliferative capacity is associated with the ability to regenerate myocardial tissue soon after birth. Recently, it has been demonstrated that 1-day-old neonatal mice do have the ability to regenerate resected cardiac tissue, and that the capacity to regenerate cardiac tissue is lost by 7 days after birth. The present commentary reviews these results and attempts to offer perspective as to how these important findings relate to current and future strategies to prevent and treat cardiac dysfunction in clinical populations.