To correlate anatomy with hemodynamics, the angiocardiographic findings were reviewed in 42 patients with common ventricle (CV). Nine had normally related great arteries (NRGA), 12 d-malposition, 21 l-malposition and 5 a common atrioventricular valve. Selective outlet chamber (OLC) angiocardiograms were available in 14 out of 29 patients with OLCs. OLC position varied from anterior and to the right of the CV to posterior and to the left of it; two categories (anterior and lateral OLC) were delineated by a line 45 degrees to theleft of anterior in the horizontal plane. The OLC was anterior in all patients with NRGA, lateral in most l-malpositions, and almost equally divided between anterior and lateral in d-malposition (P less than 0.05). Complete hemodynamic data were obtained in 29 patients. Complete mixing of venous return occurred in four patients with atresia of one valve. In the remainder complete mixing occurred in 36%, unfavorable streaming in 12% and favorable streaming in 52%. Semilunar valve position and pulmonary stenosis did not affect the nature of mixing. Systemic arterial (SA) minus pulmonary arterial O2 saturation was positive and significantly higher in patients with malposition with lateral OLCs than anterior OLCs (P less than 0.001). However 79% of SA O2 saturation variation could be predicted from pulmonary and systemic blood flow alone.