The precise method of surgical repair of double outlet right ventricle depends both on the relation of the interventricular communication to the cardiac outlets and on the course and insertion of the atrioventricular valve tension apparatus. It may be difficult to connect the interventricular communication with one or other outlet or both either because the interventricular communication is too far from the outlets or because atrioventricular tension apparatus interposes between them. This study was carried out in order to establish whether these details could be recognised preoperatively using cross sectional echocardiography. Forty two echocardiograms were reviewed retrospectively from patients with double outlet right ventricle, excluding those with atrioventricular septal defects and atrioventricular discordance. Ten further such patients were studied prospectively. The diagnosis was confirmed at open heart surgery in 19 patients. The relation of the great arteries and their outlet tracts to each other and to the interventricular communication was readily and accurately predicted. Four patients (7.7%) had no infundibular septum. The remaining 48 had such a septum. In 27 (52%) the interventricular communication was overridden by a great artery. In 14 (27%) it was roofed by the ventriculoinfundibular fold, and in 11 (21%) it was confined to the inlet or trabecular septa. The insertion of chordae tendineae limited the possible surgical options in 12 patients (23.1%) who were distributed unpredictably among the above groups. Four patients had straddling atrioventricular valves. In five, tricuspid tension apparatus inserted into the underside of the infundibular septum and, in two, into the roof of the defect. In one patient the mitral valve inserted into the defect floor. Tricuspid tension apparatus inserted into the floor of the defect in a further nine patients, but this does not compromise surgery. Thus in double outlet right ventricle cross sectional echocardiography can provide unique information necessary for planning of rational surgical management.