The quintessence of the making of the heart

In my Mannheimer lecture, designed to meet the needs of a mainly clinical audience, I present aspects of cardiac development that link basic science to clinically relevant problems. During development of the cardiac tube, and its subsequent changes as a dextrally looped structure, which is still connected to the dorsal body wall by a venous and an arterial pole, there are basic requirements. These consist of the development of myocardium, endocardium and the interposed cardiac jelly from the cardiogenic plates. In this primitive heart tube, septation and valvar formation then take place to convert it into a four-chambered heart. I demonstrate that the refining of the above events cannot take place without the addition of extracardiac populations of cells. These are presented as the "quintessence of heart development", and consist of cells derived from the neural crest, along with epicardially derived cells. Without these contributions, the embryos uniformly die of cardiac insufficiency. Important contributions are made by the cells derived from the neural crest to septation and the formation of the arterial valves, and possibly in differentiation of the central conduction system. The epicardially derived cells are essential for formation of the interstitial fibroblasts and the myocardium, as well as the coronary vascular system. I conclude by discussing specific malformations of the heart that might be linked to these extracardiac contributions.