Defects in development of the heart valves and their precursors (the endocardial cushions) are responsible for a significant percentage of congenital heart malformations in neonates. Researchers in the division are working to identify the genetic and physiologic factors which regulate development of these structures. The image above shows the heart of a 16 day old zebrafish. The two developing atrioventricular valve leaflets are seen in the center of the image and express a mesenchymal marker, Vimentin, shown in red. The valves point towards the ventricle in the lower half of the image. (Image courtesy of the Bartman Lab.)