Background: Atrioventricular septal defect with only ventricular component of septal deficiency is the least common of various forms of this malformation. We reviewed its morphology in heart specimens and compared our findings with the other forms for a better understanding of its surgical morphology.

Methods: We examined 78 cardiac specimens with atrioventricular septal defect; 56 (72%) had common atrioventricular valvar orifice with both atrial and ventricular components (so-called “complete” form), while 22 (28%) had separate valvar orifices (so-called “partial” or “incomplete” form) with 17 having only atrial component (so-called “ostium primum” form) and 5 having only ventricular component.

Results: Amongst hearts with atrioventricular septal defect, the hearts with only ventricular component of the defect had the mildest deformity of the ventricular mass characterised by less inlet-outlet disproportion, smaller “gap” between anterior and posterior parts of the atrioventricular junction and the least extensive septal deficiency. However, these hearts still possessed the characteristic common atrioventricular junction and had five-leaflet configuration of the atrioventricular valve with similar proportions of mural leaflets in both valvar orifices as in other forms. Furthermore, owing to the unique relationship of the bridging leaflets to the septum, the leaflets were always ‘upwardly’ displaced as opposed to ‘downwardly’ displaced leaflets in “ostium primum” form.

Conclusions: Our observations suggest this entity might represent the mildest end of the whole spectrum of hearts with atrioventricular septal defect. Since ‘upwardly’ displaced leaflets are not modifiable and could be aggravated further following surgery, they might play a role in late valvar dysfunction.