[Pathogenesis of congenital heart defects: fiction and truth]

This is a review based on a description of a standardized method (microdissection + SEM) for study of human and animal cardiac development. Two examples of the analytical approach are given. In the first one, concerning the establishment of contact between the aorta and the left ventricle, the previous assumptions for "vectorial bulbus rotation" are disproved by more precise observations of normal cardiac development. Aorta is not transferred into the left ventricle but is connected to it by means of a "conduit" (aortic vestibulum) delimited by the fusion of the conotruncus ridges. For the second example the multilevel-analysis of pathogenesis of conotruncus septum defects in Keeshond dogs was selected. At the organ level, hypoplasia of the right ventricle was diagnosed, accompanied by hypoplasia of conus cushions. Tissue-level analysis indicated that the major cause of these hypoplasias is a decreased relative volume of the myocardium. Further study at the cell level showed that the number of mesenchymal cells in certain parts of conotruncus cushions is also diminished. Combining these observations with what is known about the architecture of cell proliferation in the embryonic heart, allows to formulate a hypothesis on a selective lesion of the right proliferation center, as one of the main causes of the observed anomalies. Further progress towards the subcellular and molecular level will help to complete the pathway from a gene defect toward an organ defect.