Four infants with congenital heart disease showed in their first months of life poor weight gain in spite of the absence of cardiac failure; a diagnosis of intolerance to cow's milk proteins was made on the basis of laboratory findings and subsequently confirmed by the success of the avoidance diet and the positivity of the challenge tests; all four children had previously received nasogastric feeding, and this may represent a favouring factor for sensitization. Intolerance to cow's milk proteins should be considered as a possible cofactor for failure to thrive in infants with congenital heart disease.