Atrioventricular valve diverticulum--an unusual congenital malformation.

A previously unreported congenital malformation was noted in an infant with right atrial isomerism ("asplenia syndrome"). The superior bridging leaflet of a common atrioventricular valve was attached to a band of muscular tissue spanning the atrioventricular junction. A large ventricular diverticulum extended into the substance of this band, possibly due to traction during fetal life.