Summary Background & aims Infants with congenital heart disease (CHD) have elevated energy expenditure; however, they also have poor sucking and fluid restriction, which act as barriers to the delivery of adequate nutrition. The objective of this study was to investigate the effects of a high density formula (HDF) on safety, weight gain, and nutrient intake in CHD infants. Methods We conducted a retrospective analysis of 21 CHD infants, comparing between two 4-week periods in which the children were given a standard density formula (SDF; 0.67 kcal/ml) and then a high density formula (HDF; 0.77–1.03 kcal/ml), respectively. In these children, we analyzed both safety parameters (serum creatinine, BUN, AST, ALT, and the frequencies of vomiting and diarrhea) and effective parameters (energy and protein intake, fluid volume, weight gain, and serum albumin). Results The mean concentration of formula in the HDF period was 1.21 times greater than that in the SDF period. Energy and protein intake per body weight, weight gain, and serum albumin in the HDF period were significantly higher than in the SDF period. There was no clinical evidence of any adverse effects related to the HDF. Conclusion Use of an HDF formulation is able to safely increase nutrient intake and promote weight gain in CHD infants. This nutritional formulation could potentially prevent malnutrition and failure to thrive in CHD infants.