The catheterization data including angiocardiography of 30 infants and children with different types of univentricular heart were used to study the influence of pulmonary and systemic flow as well as the position of the outlet chamber on systemic arterial saturation. All patients with normally connected great arteries displayed favourable streaming and differed significantly from those with 1-TGA as well as d-TGA, who showed varying streaming characteristics. Taking into account, however, the position of the outlet chamber, favourable streaming could be demonstrated to occur in most patients with TGA and lateral outlet chamber, and significantly less in patients with TGA and anterior outlet chamber. The influence of pulmonary and systemic flow on systemic arterial oxygen saturation was obvious only in the group with complete mixing and not in those patients, where arterial saturation was affected favourably or unfavourably by interindividual streaming differences. As expected, in patients with pulmonary stenosis the pulmonary flow was determined primarily by the degree of obstruction between ventricle and pulmonary artery. Reduced perfusion of the lungs in pulmonary stenosis does not result in increased perfusion of the systemic circulation. These results indicate that in patients with univentricular heart and ventriculo-arterial discordance, a pulmonary stenosis combined with lateral outlet chamber offers the most favourable outlook with regard to natural history.