Atrial septal defects are L → R shunt lesions, with symptoms depending on the size of the shunt. Small shunts might be asymptomatic and remain undetected until adult age. Long-standing or large shunts can cause congestive heart failure, pulmonary hypertension and shunt reversal (Eisenmenger’s syndrome). The influence of anaesthesia on atrial pressures to change shunt volume is limited. Anaesthetic management therefore is to maintain preload and manage complications such as congestive heart failure or pulmonary hypertension. Large shunt volumes can cause right atrial dilatation which can lead to arrhythmias.