SPECIAL ARTICLE

It is no longer necessary to guess at why embryonic malformations occur. Techniques are now available to test almost any hypothesis concerning developmental phenomena. These include the entire armamentarium of modern cell biology: organ and tissue culture, microsurgery, time-lapse cinematography, autoradiography, and many other related methodologies. The developmental events which lead to the formation of a functional heart in the early embryo can be analyzed with these techniques. Of the pertinent questions concerning developmental processes related to congenital heart disease, those of dextrocardia and differential growth, ventricular septal defects, and cell migration and adhesion in cardiogenesis are discussed. Several experimental systems useful for attacking these questions are described. Relative growth of specific segments of the primitive tubular heart contributed by the right and left wings of the cardiogenic crescent has been examined to elucidate the mechanism of dextral looping of the tube. Migration of precardiac cells to form the heart has been traced with cinematography in the intact embryo, and by following movements of cells labeled in situ with tritium using autoradiographic techniques. To analyze the mechanisms of guidance of such cells, endoderm plus adherent precardiac mesoderm can be explanted and manipulated in tissue culture.