Why does congenital heart disease cause failure to thrive?

Metabolisable energy intake, determined by bomb calorimetry of food, vomit, stool and urine, and resting metabolism, assessed by respiratory gas exchange, were studied in 21 infants with congenital heart disease and nine control infants. Weight for age, growth rates, and daily metabolisable energy intake per kg tended to be lower in infants with heart disease than in control infants. Resting oxygen consumption was high in those infants with pulmonary hypertension and persistent cardiac failure. Energy intake, as a percentage of that recommended for age, correlated with weight gain, and resting oxygen consumption correlated inversely with both percentage body mass index and relative fatness. Failure to thrive in infants with congenital heart disease may be due to a combination of low energy intakes and, in some cases, high energy requirements allowing insufficient energy for normal growth. Increasing the energy intakes of infants with congenital heart disease may be a way of improving their growth.