BACKGROUND Congenital heart defects (CHDs) are the most common congenital malformations, often requiring surgical intervention during the early neonatal period. Although most children with CHDs are born at full term with appropriate birth weights, many of them develop malnutrition during the first weeks of life, resulting in complications after cardiac surgery. This study aimed to provide new insights into personalized nutritional interventions based on variations in breast milk (BM) composition