FIG 69.4 Close-up view of the absent atrioventricular connection that is the essence of tricuspid atresia The probe has been passed through the “dimple” in the floor of the blind-ending right atrium It enters the left ventricular outflow tract, since the dimple overlies that atrioventricular component of the membranous septum The cavity of the right atrium has no connection with the hypoplastic cavity of the incomplete right ventricle (dotted lines) FIG 69.5 Rare combination of absence of the right atrioventricular (RAV) connection (dotted lines) but with straddling and overriding of the left atrioventricular valve (LAVV) This produces an atrioventricular connection that is uniatrial but biventricular The left ventricle (LV) is the dominant ventricle, but both ventricles are incomplete FIG 69.6 Combinations of atrial arrangement (top row), atrioventricular (AV) connections (middle row), and ventricular morphology (bottom row) that produce the hearts with univentricular AV connections As shown in the bottom row, only those rare variants with the solitary and indeterminate variant can properly be described as having “single ventricles” or being “univentricular hearts.” LV, Left ventricle; RV, right ventricle