The authors report a case of Double Mitral Orifice (DMO), existing in isolation and type 3 by the Floch Prigent classification. This rare anomaly is often associated with another congenital malformation, dominated by intra-atrio-ventricular defect. Two-dimensional echocardiography is the essential diagnostic factor. Hemodynamic consequences may be nil, but mitral insufficiency and/or stenosis may complicate this malformation. Treatment may be summarised as abstention, surgical repair or valve replacement, according to the severity of lesions.