In order to investigate the basis of ventricular dysfunction in patients with univentricular heart, cineangiograms of 20 patients aged between 3 weeks and 22 years were digitized frame by frame and compared with left ventriculograms of patients with other cardiac malformations. Ejection fraction was at least normal (58% to 95%) and peak rate of systolic minor axis shortening was normal in all. However in only 3 patients was the change in volume achieved by virtue of the normal change in cavity shape; in 17 the end-systolic outline was abnormally circular and shape index, 4 pi (area)/(perimeter)2, changed by less than normal (p less than 0.01). In addition, abnormalities of regional wall movement were found in 12 patients. 11 showed a consistent pattern, unlike that found in ischaemic heart disease or other congenital lesions, of delayed systolic inward movement of the antero-apical wall, associated in 9 with hypokinesis. Four of these showed secondary delay of relaxation in the same region. One patient had an isolated abnormality of isovolumic relaxation. These findings were independent of age, volume overload or degree of cyanosis, but were more common in patients with absent atrioventricular connexion. We conclude that the architectural abnormalities in univentricular hearts lead to disturbances of myocardial function which particularly affect the apex. These are detectable from an early age.