Relating normal human cardiac development to the anatomical findings in the congenitally malformed heart.

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A proper appreciation of cardiac development can now provide the necessary background to understand the anatomical findings in the congenitally malformed heart. We recently presented an account of human cardiac development based on reconstructions of histological datasets from human embryos aged between 3.5 and 8 weeks subsequent to conception. In this review, we summarize the changes observed relative to the findings when the heart is congenitally malformed. Beginning at the stage when it is first possible to recognize the primary heart tube, we describe the looping of its ventricular component, which occurs in the 5th week. We proceed with discussion of the formation of the atrial and ventricular chambers in the 6th week. The phases are successive, albeit partially overlapping. Separation of the circulations at the venous pole is completed at stage 17, equivalent to almost 6 weeks of development. During stages representing the 7th week of development, we concentrate on the remodeling of the outflow tract. This involves initially septation, but then separation of the developing circulations. The changes involve incorporation of the proximal outflow tract into the ventricles, with formation of the arterial roots in its middle part, and addition of a distal non-myocardial component to produce the intrapericardial arterial trunks. We pay particular attention to the changes occurring during remodeling of the interventricular foramen. We show that an understanding of this process provides the basis for understanding the functionally univentricular heart, as well as the arrangement found in double outlet right ventricle.