Objective: To explore the effects of breast milk feeding and formula milk feeding on infants after cardiac surgery in the cardiac intensive care unit (ICU). Methods: Infants who underwent cardiac surgery in our ICU were divided into two groups, according to feeding type. Breast milk feeding and formula milk feeding were separately implemented in the two groups, and the remaining treatment regimens were the same. The related clinical data and feeding effects were recorded and compared. Results: The prealbumin (147.3 ± 15.2 versus 121.5 ± 18.3mg/L) and albumin (46.4 ± 4.2 versus 40.5 ± 5.1 g/L) levels in the breast milk feeding group were better than those in the formula milk feeding group (P < .05). Infants in the breast milk feeding group achieved a better total enteral nutrition time (3.0 ± 1.2 versus 5.2 ± 2.1 d), average daily weight gain (19.0 ± 3.4 versus 14.4 ± 2.3 g/kg·d), length of ICU stay (6.0 ± 2.2 versus 8.1 ± 2.9 d) and length of hospital stay (13.9 ± 4.2 versus 17.8 ± 5.6 d) than those in the formula milk feeding group (P < .05). The incidence of complications such as feeding intolerance, anemia, dyspeptic diarrhea, and nosocomial infection was lower in the breast milk feeding group than in the formula milk feeding group (P < 0.05). Conclusion: Breast milk feeding has a definite nutritional effect on infants after cardiac surgery. It is better than formula milk feeding, making it worthy of popularization and application.