A newborn girl was referred for a suspected abnormal pulmonary venous return in coronary sinus. Echocardiogram revealed a large outpouching of the left ventricle creating an accessory cardiac chamber that was connected to the left ventricle behind the mural leaflet of the mitral valve, and with the right atrium via the coronary sinus. Ten years later, the orifice between the submitral aneurysm and the left ventricle was closed percutaneously.