The spectrum of anomalies in hearts having a univentricular atrioventricular (AV) connection was examined by two-dimensional echocardiography in 183 patients and the anatomic findings were compared with angiography. The mode of AV connection was found to be of three types: double inlet via two AV valves; single inlet via one AV valve with absence of the other (left or right AV valve atresia); and common inlet via a common AV valve. Identification of an accessory chamber by two-dimensional echocardiography was possible with 90% sensitivity, but it was limited compared with angiography in patients with severely hypoplastic anterior chambers and pulmonary valve atresia. All patients with subaortic outlet foramen obstruction were detected. Great artery position and the presence of obstruction to pulmonary flow were correctly predicted in all but one patient. Two-dimensional echocardiography was superior to angiography for the detection of AV valve abnormalities which were present in 27% and included abnormal chordae, hypoplasia or dysplasia of either valve. Two-dimensional echocardiography should play an essential role in the complete preoperative assessment of patients with univentricular AV connection.