Fourteen infants with congenital heart disease were investigated for failure to thrive. Assessment of intestinal function revealed minor absorptive abnormalities (mild steatorrhea in three patients, bile salt loss in four patients), delayed gastric emptying, and abnormal triglyceride loading tests. Low caloric intake (88.3 +/- 19.3 kcal/kg/day) seemed the main reason for failure to gain weight. Weight accession and cardiorespiratory rates were monitored daily during voluntary intake, a high-caloric diet by mouth, and nasogastric tube feeding. Providing 169 +/- 29 kcal/kg/day by tube resulted in weight gain with mild and transient elevation of respiratory rate at the end of the meal and increased heart rate 90 min after the meal. This regimen is a metabolically inexpensive and efficient method of supporting weight gain in children with congenital heart disease.