A 48-year-old woman with recurrent syncope presented with acute left vision loss after another syncopal fall. She reported no prodromal symptoms and no prior syncope workup. Vital signs were normal. Ophthalmologic exam revealed left corneal ulcerations. Cardiopulmonary and neurologic examinations were unremarkable. Brain MRI, carotid ultrasound, serial troponins, telemetry, and EKG were normal. Transthoracic echocardiography uncovered a diagnosis of cor triatriatum, an obstructing patent membrane in a dilated, bisected left atrium (Fig. 1) with constricted blood flow and increased flow velocity across the restrictive orifice (Fig. 2).

Fig. 1
figure 1

Transthoracic echocardiographic image (apical 4-chamber view) displaying a thin, linear membrane (orange arrow), traversing and dividing the left atrium into two abnormal left atrial chambers (labeled as LA 1 proximally and LA 2 distally). LA left atrium, LV left ventricle, RA right atrium, RV right ventricle

Fig. 2
figure 2

Transthoracic echocardiographic image (apical 2-chamber view, color-flow Doppler mode) demonstrating constricted blood flow and increased flow velocity (orange arrow) across the restricted opening in the left atrium caused by the cor triatriatum

Cor triatriatum represents only 0.1–0.4% of congenital cardiac malformations and has several anatomic variants.1,2 Ventricular inflow obstruction results from abnormal septation within the left or right atrium, creating two atrial chambers subdivided by a thin membrane. Many remain asymptomatic until their thirties. Most cases in adulthood are discovered incidentally.3,4,5 Clinicians should suspect cor triatriatum in young healthy patients with clinical features mimicking mitral stenosis but no cardiovascular co-morbidities. Early and severe manifestations occur in smaller communicating orifices and higher obstruction between bisected atrial chambers.1 Late symptoms results from progressive increase in pulmonary artery pressure.2 Syncope, heart failure, and sudden cardiac arrest are well cited.5,6 Early diagnosis by echocardiography is important to expedite surgical cure.2,7,8