A noninvasive procedure for diagnosis and quantitation of right-to-left intracardiac shunts will enhance the management of patients with cyanotic congenital heart disease. This study describes an application of radionuclide (RN) angiocardiography for quantitation of right-to-left shunt amount. Gamma variate model was fitted to radionuclide data recorded over the carotid artery. Data analysis was performed retrospectively in 35 patients who underwent cardiac catheterization within a week from the day of RN angiocardiography. Thirty one of the patient had right-to-left shunts and 4 of them had left-to-right shunts. Both the radionuclide and Fick measurements correlated well (r=0.93, 0.93, 0.89, p<0.01 in each measurements). Therefore, RN angiocardiography data may be used for accurate calculation of right-to-left shunts in cyanotic congenital heart disease patients.