We studied ventricular volumes and ejection fraction by radionuclide angiography (equilibrium technique) in 15 patients (aged 3-48 years) with double inlet ventricle not yet submitted to corrective surgery. The end-diastolic volume (measured in nine cases) ranged from 108 to 219 ml/m2 (156 +/- 32), being lower than the normal theoretical value (right plus left ventricle) in six cases. Ejection fraction ranged from 30 to 77% (56.4 +/- 13). The value was significantly higher in the subgroup of 10 patients with a dominant left ventricle as compared to the five cases with dominant right or indeterminate ventricular morphology (63.2 +/- 8.3 versus 42.8 +/- 9, P less than 0.01). In seven of the 15 patients, measurements were obtained both at rest and during dynamic exercise in the semi-upright position. The end-diastolic and end-systolic volumes, stroke volume, ejection fraction underwent a slight non-significant reduction (from 158 +/- 29 to 147 +/- 24 ml/m2, from 58 +/- 16 to 56 +/- 24 ml/m2, from 100 +/- 27 to 90 +/- 24 ml/m2, from 64% +/- 9 to 61% +/- 13). During exercise, ventricular volumes mostly behaved as follows: slight reduction of end-systolic volume, decrease of end-diastolic volume, no increase (no change or decrease) of ejection fraction.(ABSTRACT TRUNCATED AT 250 WORDS)