To determine the spectrum and associated anomalies of double inlet ventricle (single ventricle), echocardiographic data of 50 patients with double inlet ventricle were reviewed and compared with the data obtained by cardiac catheterization, cardiac surgery and autopsy. Standard echocardiographic planes were used to determine the cardiac anatomy and the size of the interventricular communication. Double inlet by way of two perforate valves was found in 44 patients. In 42 of the 44 patients the dominant ventricular morphology was of the left ventricular type (double inlet left ventricle); in 13 of these 42 patients stenosis of one atrioventricular (AV) valve was found. Double inlet right ventricle and double inlet indeterminate ventricle were each found in one patient. Double inlet by way of a common AV valve was found in six patients, all of whom had atrial isomerism. The diagnosis of double inlet ventricle was accurate by two-dimensional echocardiography in all 44 patients. A restrictive interventricular communication was shown in 13 patients and a nonrestrictive communication in 17 patients by cardiac catheterization. Patients with a restrictive interventricular communication had a significantly smaller interventricular communication area normalized by the body surface area (mean +/- SD 1.21 +/- 0.53 cm2/m2) than did those with a nonrestrictive interventricular communication (2.33 +/- 0.71 cm2/m2) (p less than 0.01). Infants with an aortic anomaly had a significantly smaller interventricular communication area (1.35 +/- 0.65 cm2/m2) than did those without an aortic anomaly (2.57 +/- 0.76 cm2/m2) (p less than 0.05). Echocardiography provides an accurate noninvasive diagnosis in patients with double inlet ventricle, offering reliable information about the restrictive interventricular communication.