The heart is the first organ to form and function during vertebrate development. Heart development is an elaborate process requiring cell specification, cell differentiation, cell migration, morphogenesis and interactions among cells from several embryonic origins. Entry of cells into the cardiac lineage in response to the appropriate signals is coupled to the expression of a set of transcription factors that initiates the program for cardiac gene expression and drives the morphogenic events involved in formation of the multi-chambered heart. The left ventricle is derived from the classical primary heart field, while the right ventricle and outflow tract are derived from a distinct second heart field. Some of the earliest expressed transcription factors that initiate cardiac fate are the homeobox transcription factor NKX2...