Regulates the chamber-specific expression of myosin isoforms by activating the expression of the ventricle myosin heavy chain-1 (Vmhc1) and suppressing the expression of the atrial myosin heavy chain-1 (Amhc1) in the ventricles. May play a critical role in establishing chamber-specific gene expression in the developing heart. Ventricles of the heart, developing feather buds, retina, hindbrain. All stages of heart development. Belongs to the TALE/IRO homeobox family.