RESUMEN
A patient is presented who had cor triatriatum documented with angiography and surgery. On echocardiographic study, an abnormal, dense linear echo on "sector scan" was consistently seen to traverse the left atrial cavity obliquely; the ends of the echo were attached to the posterior aortic and lateral walls of the left atrium. In addition, high frequency oscillatory movements were evident in the echo of the posterior mitral cusp. Both echocardiographic features disappeared promptly after successful resection of the intraatrial fibrinous membrane. This experience indicates that in the presence of strong evidence of mitral stenosis, an unexpectedly normal mitral valve echogram should initiate a thorough echographic search for cor triatriatum, a treatable cardiac malformation whose diagnosis can easily be missed on "routine" echocardiographic studies.