The authors examined the level of the atrio-natriuretic factor (ANF) in 7 infants with inborn heart disease at the age of 3 weeks to 5.5 months. As controls they examined 9 convalescent infants aged 1-10 months. Congenital heart disease was confirmed by clinical methods (ECG and X-ray) and echocardiographically (one-dimensional, two-dimensional and pulsed Doppler echocardiography, 5MHz probe, Kontron Co.). Although a small group is involved, elevated ANF values were recorded in infants with inborn heart disease, as compared with controls.