Study investigators will develop a biomarker-based EN decision rule for post-operative infants with CHD. Investigators lack objective data to inform decisions regarding provision of EN, an area where subjective decision-making is currently the rule. Lack of standardized practices for post-operative feeding lead to EN practice variation, which may harm these infants with regard to septic morbidity and long-term neurocognitive outcomes. Study investigators will address gaps in knowledge regarding the emerging role of the gastrointestinal tract as a modulator of SIRS, sepsis, and organ dysfunction after CPB during childhood. Finally, this proposal will inform the design of future studies to provide individualized, safe EN support, targeted to intestinal EBF. This proposal presents several innovations. First, the investigators will explore the gastrointestinal tract as a way to improve post-operative outcomes after surgical repair of CHD in infants. Second, the investigators will develop a feeding intolerance scale for use in future studies of EN titration in infants with CHD. Third, this proposal prospectively evaluates biomarkers of intestinal EBF in infants with CHD, a major advance in biomarker development in this field.