Radionuclide angiography provides a reliable and extremely rapid technic for assessing the physiologic and pathologic features of cardiovascular malformations. Eighty-six infants and children and seven adults have been studied after intravenous infusion of99mtechnetium with a scintillation camera coupled to a computer-tape storage system. Pulmonary vascular isotope-dilution curves detected the presence or absence of left-to-right intra- or extracardiac shunts with great sensitivity. Therefore, the method has especially widespread applicability in the distinction between organic and innocent heart murmurs, in the evaluation of postoperative patients, and in the assessment of the natural course of selected, specific malformations. Moreover, also without resorting to cardiac catheterization, scintillation scanning is capable of defining great artery orientation and position, cardiac chamber position, approximate chamber volumes, and the distribution of pulmonary arterial blood flow. The method described is technically simple, without known risk, is easily applicable to large numbers of patients, and provides clinically important information concerning many forms of congenital heart disease.