Background: Children with congenital heart disease (CHD) are prone to weakening and underweight. 
Objectives: We aimed to evaluate the effect of high-density formula on weight gain and gastrointestinal intolerance in CHD children following heart surgery.
Methods: All randomized clinical trials (RCTs) on weight gain following heart surgery in CHD children were systematically searched on Web of Science, PubMed, and Scopus databases by related keywords from 1990/01/01:2022/12/30. Papers in languages other than English were excluded. Among 11 trials that evaluated the effect of a high-density formula on weight, 6 studies were excluded due to their study samples (older than 2 years) and using macronutrients to enrich the formula.
Results: Finally, 5 eligible trials with a total of 278 participants were included in this systematic review. The follow-up duration ranged from 5 to 30 days. Among 5 included studies, 4 indicated that feeding with high-density or concentrated formula can improve weight gain in children with CHD compared to the standard formula. Diarrhea was the most common gastrointestinal complication associated with the high-density formula, although its frequency was low.
Conclusions: Feeding with a high-density formula or concentrated standard formula could be an inexpensive and practical way to fulfill the nutritional requirements of CHD children following surgery, which can lead to more weight gain without any significant gastrointestinal side effects.