The abnormal origin of the left coronary artery from the trunk of the pulmonary artery is rarely encountered, difficult to diagnose and has a severe prognosis because of the major risk of sudden death. The authors report the case of a 63 year-old male patient, presenting this anomaly which creates a true left-to-right shunt with myocardial ischemia secondary to the steal of coronary blood toward the pulmonary artery. The diagnosis is evoked by bidimensional cardiac sonography, pulsated and color Doppler, which permit to confirm the left-to-right shunt while this is confirmed by coronary angiography. The treatment is essentially surgical.