The purpose of this randomized trial is to clarify the role of enteral nutrition (EN) on the relationship between cardiopulmonary bypass-induced inflammation and insulin resistance by investigating the effects of two different feeding strategies in infants following cardiac surgery. The study's primary objective is to determine if early and higher volume feeding modifies the relationship between the severity of postoperative systemic inflammation and insulin resistance.

Good nutrition is important for patients after surgery. Patients who are given food tend to have fewer infections, better wound healing, and are possibly discharged more quickly from the intensive care unit and hospital. However, the best time to start feeds and the speed at which they can be increased is unclear. This may be particularly true for young children who have undergone heart surgery using a heart-lung bypass machine (bypass surgery). Bypass surgery can cause inflammation that can change the way the body uses energy and nutrients. Specifically, after bypass the body can become insensitive to insulin (insulin resistant), which means that the cells in the body don't take up sugar from the blood like they are supposed to, and this may lead to complications from the surgery. In a recent study we found that inflammation and insulin resistance was not associated with as many complications in children who were being fed. We are not sure if feeding changed the way in which the body responded after surgery or if doctors chose to feed only patients who were already recovering well. In general, doctors often hesitate to feed patients immediately after surgery because they worry that the body may not be ready for food although there is not much information to prove that this worry is correct. Starting feeds early using a structured feeding plan may be good during the recovery from heart surgery, even in our most vulnerable patients. We therefore designed this study to see if starting feeds early after bypass surgery and increasing them more quickly than our usual routine would decrease inflammation and insulin resistance. We will only study children younger than 6 months of age because they are at higher risk of complications from bypass surgery.

Inclusion Criteria:

• less than 6 months of age
• weight > 2.5kg
• surgery using cardiopulmonary bypass
• expected duration of ventilation > 6 hours

Exclusion Criteria:

• cardiac transplantation
• prematurity (<37 weeks gestation AND under 28 days of life)
• intrauterine growth restriction
• NEC
• structural gastrointestinal anomalies
• known preoperative feeding intolerance
• diabetes or known metabolic disorder
• preoperative liver or renal dysfunction
• postoperative contraindication to enteral feeding as determined by clinical team
• previous enrollment at an earlier operation
• in the opinion of the clinical or research team the patient is too well to participate, such that slow escalation to feeds would lead to hunger and therefore be considered inappropriate.