Sixty-two children investigated by cardiac angiography for a wide spectrum of congenital heart disease were randomly assigned to one of two groups, one for iohexol, 350 mg I/ml (Omnipaque, Nycomed UK Ltd) and one for iopamidol, 370 mg I/ml (Niopam, E. Merck Ltd). Changes in systolic pressure, end-diastolic pressure when the injection was made into a ventricle, heart rate and rhythm and plasma osmolality were assessed at 1 min and 3 min after the injection of contrast medium. The angiograms were subjectively assessed for angiographic quality. No significant differences were detected between the two groups.