Congenital heart disease (CHD) is one of the most common birth defects in the UK. Children with CHD are at risk of underfeeding and undernutrition. This is due to both the increased nutritional requirements of the disease and sometimes clinical management, which often hinders delivery of optimal nutrition.There are as yet no studies assessing micronutrient body stores in children with CHD or whether micronutrient deficiencies predict poor clinical outcomes, such as post-operative complications, after major cardiac operations.