Plays an essential role in cardiac morphogenesis. Efficient DNA binding requires dimerization with another bHLH protein. Highly expressed in the adult heart and expressed at lower levels in the intestine and gall bladder. At stage 15, detectable in the anterior and ventral mesoderm near the heart primordia. At stage 22, the central band of expression in the lateral plate mesoderm is confined to the mid-embryo. By stages 28-30 (late tailbud stages), the region of expression in the lateral plate mesoderm has expanded into a symmetrical arc of ventral and lateral expression, which fuses in the midline where the straight heart tube has formed. At stage 33 (beginning of heart looping), expressed in the heart, lateral mesoderm and branchial arches. At stage 37, uniform expression in the myocardium and cardiac outflow. Most abundant in the heart and outflow tract at stage 47 (tadpole stage). By bone morphogenetic proteins BMP-2 and BMP-4.