Truncus arteriosus is a vascular abnormality with the pulmonary artery and the aorta arising from a common trunk with a single valve, resulting in a large L → R shunt with mixing. Associated lesions are a ventricular septal defect and coronary anomalies. The lesion causes cyanosis, pulmonary hypertension and congestive heart failure. As with every L → R shunt pulmonary vascular resistance should be kept high with air and mild hypoventilation and an increase in systemic vascular resistance should be avoided. Inotropes might be needed for heart failure.