Although clinically silent in the majority of cases, enlarged bronchial arteries or systemic-to-pulmonary collateral arteries may complicate congenital heart disease in infants, causing significant left-to-right shunting with subsequent pulmonary congestion and respiratory compromise. So far, pulmonary haemorrhage, a well-known complication in older patients with cyanotic congenital heart disease, has not been described in infancy. We describe the case of a 6-month-old girl with tetralogy of Fallot and absent pulmonary valve who developed haemoptysis with severe respiratory distress following corrective surgery of the cardiac malformation. High-resolution computed tomography of the thorax followed by selective angiography revealed a systemic-to-pulmonary collateral artery originating from the left internal mammary artery. Pulmonary haemorrhage stopped immediately following coil occlusion of the collateral. A second episode of pulmonary haemorrhage occurred at the age of 9 months during mechanical ventilation for treatment of pneumonia. Repeat angiography revealed two more collateral vessels. Again coil occlusion resulted in prompt resolution of pulmonary haemorrhage. According to our experience, enlarged bronchial arteries or systemic-to-pulmonary collateral arteries should be considered in infants with cyanotic heart disease with unexplained pulmonary congestion or prolonged respiratory problems.