cor triatriatum

[trī-ā′trē-ātəm]
n.
  1. A congenital heart abnormality in which the heart has three atrial chambers, the left atrium being subdivided by a transverse septum with a single small opening that separates the openings of the pulmonary veins from the mitral valve.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.