An aortopulmonary window is a L → R shunt lesion between the ascending aorta and the pulmonary artery, with symptoms depending on the size of the shunt. The size of the window determines how quickly high output heart failure develops. The decrease in pulmonary vascular resistance in the first weeks of life increases the shunt volume and the pulmonary blood flow increases. Anaesthetic management aims to keep the shunt volume as low as possible with high pulmonary vascular resistance and a reasonably low systemic blood pressure.