The patient underwent right-sided and left-sided cardiac catheterization. Findings were as follows: mean right atrial pressure of 10 mm Hg, pulmonary artery pressures of 35/13 mm Hg (mean, 23 mm Hg), mean pulmonary capillary wedge pressure of 11 mm Hg, thermodilution cardiac output of 4.18 L/min, and calculated cardiac index of 2.86 L/min/m2. Oximetric studies showed that distal pulmonary artery saturation was 86.2%; right ventricle, 87.6%; right atrium, 87.6%; superior vena cava (SVC), 71.2%; and inferior vena cava, 73.3% consistent with 2.1:1 left to right shunt at the atrial level. Left ventriculography estimated ejection fraction at 65% without evidence of mitral regurgitation or left to right shunting. Coronary angiograms demonstrated moderate coronary artery occlusive disease not requiring intervention; aortic oxygen saturation was 96%. Transesophageal echocardiogram (TEE) did not suggest atrial septal defect (ASD) (Fig 2B). A contrast-enhanced multidimensional cardiac CT (MD-CCT) scan was obtained, and images are shown in Figure 3.