Over the past several years the central roles of several different growth factors in the normal development of the embryonic heart have been identified through a variety of techniques involving microscopy. Initially, most studies consisted of descriptions of gross changes in cardiac morphology associated with naturally occurring mutations that affected growth factor function. More recently the development of specific probes for growth factor receptors that can be used in confocal microscopy have aided in the identification of changes in the temporal and spatial distributions of receptors at various stages of development. The correlation of these changes with developmental events such as valve formation and trabeculation in the heart, in conjunction with biochemical studies and blocking agents for the growth factors have significantly increased our understanding of growth factor function in cardiac development.