The development of abnormal flow has been described in patients with incoordinate motion of the ventricular wall. In all cases so far documented, these abnormal patterns of flow have been restricted to the ventricular cavity, and the atrioventricular valve remained closed. We identified a patient after a Fontan operation in whom the degree of ventricular mural incoordination was of such severity that the atrioventricular valve remained open and atrioventricular flow occurred for 140 msec after the onset of QRS complex. As far as we know, this phenomenon has not previously been described.