Source:http://linkedlifedata.com/resource/umls/id/C0009995
MSH: A malformation of the heart in which the embryonic common PULMONARY VEIN was not incorporated into the LEFT ATRIUM leaving behind a perforated fibromuscular membrane bisecting the left atrium, a three-atrium heart. The opening between the two left atrium sections determines the degree of obstruction to pulmonary venous return, pulmonary venous and pulmonary arterial hypertension.,NCI: A rare congenital abnormality of the heart characterized by the presence of three atria. The right or left atrium is divided into two parts by fibromuscular tissue or a membrane. It may be associated with other heart congenital abnormalities.