The importance of microRNAs(miRNAs)in cardiovascular development is now broadly accepted as crucial regulators and dysregulation of their expression has been linked to cardiac disease.MicroRNA cluster miR-17-92 has been implicated in cardiac development and function,yet its defined mechanisms of action in these contexts are uncertain.We focused on miR-19b,which is a key component of the miR-17-92 cluster proven to induce cardiomyocyte proliferation in vitro.This study aimed to identify its biological significance in cardiac development and underlying molecular mechanisms.