Infants with significant left-to-right shunts due to ventricular septal defects and atrioventricular canal defects commonly present with respiratory symptoms, such as shortness of breath while feeding, tachypnea, and wheezing. Radiographs show hyperinflated lungs as well as cardiomegaly and increased vascularity. Enlarged vessels adjacent to small compressible airways as well as peribronchial interstitial edema may cause diffuse air trapping. In this study, using an automated planimetric device, we measured the total thoracic, cardiomediastinal, and lung volumes in a group of patients with large left-to-right shunts as well as in a group of normal controls and found that, as expected, all volumes were significantly increased in the abnormal group. We also tried to correlate these volumes (corrected for patient size) with the degree of left-to-right shunt and found that there was no significant correlation between the cardiac or lung volumes and shunt size as estimated by cardiac catheterization.