Certain pediatric patients undergoing surgery for the most severe forms of congenital heart disease are exposed to high doses of ionizing radiation. The amount of cumulative radiation exposure from all modalities has not yet been evaluated. The purpose of our study was to evaluate the cumulative radiation exposure in a contemporary cohort of patients with congenital heart disease undergoing single-ventricle palliation. This is a single-center, retrospective study of pediatric patients undergoing Fontan completion between May 2005 and May 2010. Radiation exposure from all procedures including cardiac catheterizations, computed tomography (CT) scans, plain film radiography, and nuclear medicine scans was evaluated. Radiation dose was calculated as the dose area product (μGy m(2)) and was measured in all cardiac catheterizations, CT scans, and other imaging modalities. Seventy patients who underwent Fontan completion at a mean age of 3.6 ± 1.5 years (range 1.4-8 years) were included in the study. Mean number of chest X-rays was 32 ± 8 (range 10-285) with a mean cumulative total exposure of 1,320 μGy m(2) (range 480-12,960) per patient. Mean number of cardiac catheterizations was 2.45 ± 1.3 (range 1-8), and mean fluoroscopy and cine angiography exposures per case were 1,103 ± 245 and 1,412 ± 273 μGy m(2) giving a mean cumulative exposure of 9,054 μGy m(2) (range 2,515-201,200) per patient for all catheterizations. Mean number of CT scans performed was 0.44 ± 0.4 (0-11), and the mean exposure was 352 μGy m(2), giving a mean cumulative total of 154 μGy m(2) (range 0-3,872) per person. A total of five lung perfusion scans were carried out. Radiation exposure in patients with congenital heart disease undergoing single-ventricle palliation is quite variable. Most of the exposure to ionizing radiation occurs during cardiac catheterization. Strategies to utilize other imaging modalities such as MRI would decrease exposure in this particular group of patients who may be particularly vulnerable to its side effects.