Extracorporeal membrane oxygenation (ECMO) is an established intervention for respiratory or cardiorespiratory support in children with congenital heart disease (CHD) when all other interventions have failed. Hyperoxia following successful resuscitation has been associated with increased mortality in pediatric and adult studies, including, specifically, hyperoxia during ECMO management. We hypothesized that this effect may be pronounced in patients with lower arterial oxygen saturation at baseline, such as those with cyanotic CHD. We aimed to determine if relative hyperoxia in children with cyanotic single ventricle circulation on Veno-Arterial (VA)- ECMO is a risk factor for mortality in a large multicenter registry analysis.