The regulation of concentration and function of growth factors is of crucial importance to proper embryonic development of the heart. The patterns of expression of three extracellular modulators of the transforming growth factor-β superfamily of growth factors, Follistatin, Follistatin-like1, and Follistatin-like3, are described with respect to heart development. Follistatin is highly localized in the endocardium covering the developing cardiac valves. Follistatin-like1 is localized in the mesenchymal filling of the pharyngeal arches and broadly expressed in cells directly bordering myocardium. Follistatin-like3 is not expressed in the heart. Taken together, these observations are suggestive for a role for Follistatin in cardiac valvulogenesis and a role for Follistatin-like1 in controlling late heart muscle cell formation. Anat Rec, 2007. © 2007 Wiley-Liss, Inc.