An infant with frequent upper airways infections presented syncopes during meals and weeping since the age of eleven months. Cardiac examination was always normal. At 14 months of age, an echocardiogram with colour Doppler demonstrated a severely stenotic isolated supramitral membrane with severe pulmonary hypertension. The membrane was immediately excised curing the malformation and suppressing definitively the syncopes, probably due to decreased cerebral blood flow during exertion. An echocardiogram should always be performed when syncopes remain unexplained in small children. It allows early diagnosis and treatment of congenital heart defects which do not have auscultatory findings especially those resulting in severe pulmonary venous obstruction.