Atresia of the left main coronary artery is a rare coronary anomaly. We describe the case of a 5-year-old child presenting in emergency in extremis. Clinical findings of haemodynamic collapse, malignant ventricular tachyarrhythmias and severe mitral regurgitation were indicative of a possible ischaemic aetiology. Surgical revascularization of the atretic left main coronary artery segment using an interposition autologous saphenous vein graft was successfully performed.