The heart is the first functioning organ to form during development. Abnormalities in heart development lead to congenital heart defects (CHDs), one of most common birth defects and major causes of infant death and severe health problems in adults. CHDs display a spectrum of clinical characteristics and lack association of responsible specific genes. Thus, understanding how the heart is formed is a critical step toward improved diagnosis and potential treatments for CHDs. The goal of our laboratory's research is to understand the genetic, molecular and cellular mechanisms that control heart morphogenesis using zebrafish as a model system. Zebrafish comprise the ideal system in which to pursue this objective because 1) the transparent and externally developed embryo permits easy observation of heart development in live embryos and high-resolution in vivo imaging, 2) power embryological, genetic, pharmacological and cellular tools are available in zebrafish and 3) embryos can develop to the larval stage without functional hearts (making it possible to study the consequences of severe heart defects). We particularly are interested in understanding 1) how two populations of myocardial precursors migrate towards to the embryonic midline to form primitive heart tube, the foundation for subsequent cardiac morphogenesis and 2) how internal organs including heart are asymmetrically placed along the left-right body axis.