Two patients with huge aortopulmonary window, both ten months-old, that showed curiously up at a clinical viewpoint, including echocardiography, as a mitral valve regurgitation with a dilated mitral ring secondary to the accentuated blood volume through it, were reported. Early signs of heart failure, accentuated systolic murmur at mitral area and overload of left heart cavities, characterized clinical impression of a congenital mitral insufficiency, in both cases. The correct diagnosis was established at operation and at necropsy study, bringing it to us the need to a more accurate analysis of the different diagnostic elements, especially in anomalies which clinical manifestations show great similarities.