The significance of insufficient intakes in the growth failure of congenital heart disease was evaluated by measuring the response to forced feeding in patients who, prior to it, had had adequate calorie intake on the basis of normal requirements for age and weight but who did not grow. The anabolic response was excellent. On a comparable calorie intake, nitrogen retention and weight gain were similar to those of patients with growth failure in the absence of organic disease. Nitrogen retentions were proportionate to the gain in weight. Calorie requirements per unit of body weight were increased because the basal metabolic rate (BMR) was increased. This increase was not due to the heart disease because control patients with similar degrees of growth failure in the absence of organic disease had a similar BMR.