Single (primitive) ventricle.

Single ventricle is that condition in which both atrioventricular (A-V) orifices enter a common ventricular sinus, from which the arterial trunks emerge with their coni. The following types of single ventricle were found: (1) with regular (noninverted) transposition in levocardia; (2) with inverted transposition in levocardia; (3) with normal position of arterial trunks in levocardia; (4) in dextrocardia, and (5) in mesocardia. This entity is differentiated from common ventricle which is basically a heart with a large ventricular septal defect. Single ventricle does not include mitral and tricuspid atresia by definition, nor does it include straddling tricuspid orifice, in which two distinct ventricles are present. The concept of single ventricle herein defined differs from de la Cruz and Miller's concept of double-inlet left ventricle which includes straddling tricuspid orifice. Embryologically in single ventricle we are dealing with persistence of the primitive state of the bulboventricular loop, due to a lack of expansion of the atrial canal to the right during the process of absorption of the bulbus.