Malnutrition (undernutrition) in children with congenital disease (CHD) is a notable concern, with preoperative and persistent growth failure post-cardiac surgery contributing to poorer outcomes. Poor growth in children with CHD in low-income environments is exacerbated by feeding difficulties, poverty, delayed diagnosis, and late corrective surgery. This study describes and compares the growth of young children with CHD undergoing cardiac surgery in central South Africa from before to 6-months after cardiac surgery.