Figure 2: miRNAs control various stages of embryonic heart development. Schematic representation of the main stages of heart development. Murine cardiomyocyte progenitors become organized into a linear heart tube at day 7.5 post coitum (left). Subsequently, atrioventricular canal specification (AVC) as well as looping and swelling of the heart gives rise to the ventricular and atrial chambers. Between E13.5 and E15.5, the structure of the heart is complete and consists of the right atrium (RA), left atrium (LA), right ventricle (RV), and left ventricle (LV). miRNAs and their downstream targets are shown during embryonic heart development. Of note, compelling evidence for a critical role of miRNAs during AVC specification has been collected only in developing models such as zebrafish. It is however plausible that particular miRNAs also play an important role in AVC specification in mammals but has not yet been elucidated.