Clinical assessment of systemic perfusion in single ventricle patients with parallel circulation can be difficult in the outpatient setting. Near infrared spectroscopy (NIRS) is a noninvasive measure of cerebral oximetry. We measured vital signs, pulse oximetry, and NIRS in 20 single ventricle patients with parallel circulation prior to routine cardiac catheterization. These variables were evaluated to determine the best noninvasive predictor of the superior vena cava saturation (SVC(sat)) as a marker for the adequacy of systemic oxygen delivery. The mean age was 6.7 months [standard deviation (SD), 8.6] and mean weight was 6.5 kg (SD, 2.2). Diagnoses were hypoplastic left heart syndrome (8), tricuspid or pulmonary atresia (10), and double-outlet right ventricle variants (2), all prior to cavo pulmonary anastomoses or complete repairs. Stepwise multiple regression analysis generated a model in which only NIRS was a significant independent predictor of SVC(sat) (p = 0.009). These results support the conclusion that NIRS can be a useful tool to evaluate awake single ventricle patients in the outpatient setting.