A congenital cardiac malformation in which there is a partition that divides the left atrium into a posterosuperior chamber that receives some or all of the pulmonary veins and an antero-inferior chamber that communicates with the left atrial appendage and atrioventricular junction (usually the mitral valve).
Additional information: in differentiating 'Divided left atrium' from 'Congenital supravalvar or intravalvar mitral ring', in the latter, the antero-inferior compartment contains only the mitral valvar orifice.