A girl and a boy, both aged 4 years, had displayed a blue discolouration of the skin for several years. In the girl, electrocardiography and roentgenography of the chest revealed no abnormalities; in the boy, the cardiac murmur was attributed to an insignificant ventricular septal defect. Further examinations were performed only when the children developed sleeping problems and decrease of exercise tolerance, respectively. In both, a right-left shunt was discovered caused by a direct communication between the right pulmonary artery and the left atrium, and tetralogy of Fallot, respectively. Both patients' condition improved after operation. Chronic central cyanosis in a child constitutes an indication for consultation of a paediatric cardiologist.