Embryology of the univentricular heart.

Controversies remain concerning the nomenclature, nature and pathogenesis of the various forms of univentricular heart. Common ventricle may well represent a very large ventricular septal defect while the nature of the indeterminate or nonspecific form of univentricular heart remains in doubt. Univentricular heart, right ventricular type, could be ascribed to overshift of the embryonic atrioventricular canal to the right, resulting in both atrioventricular ostia entering a large ventricular chamber which has the morphological characteristics of a right ventricle. In univentricular heart, left ventricular type on the other hand, the rightward shift of the atrioventricular canal appears to have failed or remained incomplete, possibly due to an abnormal position of the atrioventricular canal relative to the bulboventricular septum. Normal septation of the atrioventricular canal results in both atrioventricular ostia giving access to a large ventricle which in the main has the morphological features of a left ventricle.