The Embryology of Ventricular Flow Pathways in Man

IT IS A CURIOUS FACT that, despite the importance of congenital heart disease in modern eardiology, researeh on the emibryology of the heart holds little interest for eardiologists and clinical investigators. The reasoni for this cannot be that all cardiac developnment problems are solved, for there is seareely a single form of congenital heart disease the developmental neclhanism of whieh is coi1fidently known, and many aspects of normal heart development are still obseure. Most embryologic research in the past has been concerned with early stages of cardiac development, up to the time of closure of the initerventricular septum. But this happens durin:og the first maolnth or so of fetal life, amid we are in virtual ignorance of what liappeiis to the heart during the succeeding 8 maonths of fetal life. That cardiologists have not taken part in embryologic research might be of only passing interest were not classical emiibryologists turning away from organi differenitiatioti in their research toward mneh earlier stages, toward cellular and mnolecular embrvology. If we are to make progress in our understanding of the later developimental mechanisms responisible for congenital heart disease, clinical investigators will have to provide it. It is in the hope of demonstrating that cardiac embryologic research is an appropriate and rewarding field of research for the clinically oriented investigator that the following is written a elinieian's view of humBan cardiac development. Fronm the morphologic point of view, cardiac development has two aspects: one is the development of the flow pathwavs of the heart, and the other is the developmnent amid differenitiation of the substance of the heart, its mvoeardiunm, conduetion tissue, conneetive-tissue