Transcription factor (By similarity). Plays an essential role in cardiac morphogenesis (PubMed:8533092). Efficient DNA binding requires dimerization with another bHLH protein. At stage 8, detected in the cardiac crescent. At stage 10, expressed throughout the cardiac tube and the sinus venosus. By stage 15, expressed homogeneously in the various regions of the heart, including the atria, future left ventricle, bulbus cordis and truncus arteriosus, and in the forming branchial arches. Expression persists through stage 20, but decreases thereafter.