Chylothorax occurs in ~3 to 5 % of infants undergoing cardiac surgery. Standard treatment requires discontinuation of breast milk feeding, due to the abundance of long chain triglycerides, and transition to a medium chain triglyceride (MCT) based formula. Objective: To determine the effectiveness of fat-modified breast milk (MBM) for the treatment of chylothorax compared with MCT-formula. Hypothesis: The investigators primary hypothesis was that infants fed MBM would have more chyle drainage in the first 5 days after diagnosis compared to infants fed an MCT based formula which is the current standard of care. Design: Infants with chylothorax were eligible. Treatment infants (n=8) received mother's own milk that had been modified by removing the fat layer via centrifugation and adding MCT and nutrients to provide 67 kcal/mL and 11 g/100 mL protein (MBM group). Control infants (n=8) received an MCT-formula (MCT group). The feeding intervention was a minimum of 6 weeks after chest tube removal per The Hospital for Sick Children standard chylothorax treatment protocol. Outcome measures collected included chyle drainage from chest tubes, weight, length and head circumference measurements and estimated energy and nutrient intake.