Formation of the heart loop and proliferation structure of its wall as a base for ventricular septation.

Controversial criteria for definition and classification of univentricular hearts are discussed from the point of view of proliferation pattern in the wall of heart tube and heart loop stage. The persistence of the primitive diffuse proliferation structure is the condition for the development of univentricular heart in which the morphogenetic mechanism forming the ventricular septum does not operate. Pseudouniventricular heart, i.e. the heart with the large main chamber accompanied by a small accessory cavity, is the result of total or partial right or left hypoplasia in which the extent of operation of the above mentioned mechanism is determined by the degree of ventricular hypoplasy. The morphogenesis of the heart wall structure and relief including the atrioventricular and arterial valves is a secondary feature, mostly dependent on the changed hemodynamic conditions.