Cor triatriatum is a rare condition where the left atrium is septated by a fibro-muscular membrane, causing obstruction. Symptoms depend on degree of obstruction, from asymptomatic in minor obstruction to low cardiac output failure and pulmonary congestion with pulmonary hypertension in severe obstruction. Some cases have an associated atrial septal defect, causing a L→R shunt. Anaesthetic management needs to be adjusted to the individual lesion, avoiding tachycardia and avoiding an increase in systemic blood pressure for promoting forward flow.