A young woman with a divided left atrium.

To cite: Lopez-Ruiz N, Lince R, Ramirez B. BMJ Case Rep Published online: [please include Day Month Year] doi:10.1136/bcr-2013202008 DESCRIPTION A 19-year-old woman was sent for a twodimensional transthoracic echocardiography because of dyspnea on mild exertion of recent onset. An echocardiography revealed a membrane dividing the left atrium (LA) into a posterosuperior chamber (SC) and an anteroinferior chamber (IC) (figure 1A, video 1). However, no Doppler colour flow acceleration (figure 1B, video 2) or pressure gradient was noted. LA appendage was included in IC (figure 1C). The right heart and pulmonary artery pressure were both normal. A threedimensional echocardiography showed the membrane in greater detail and revealed the orifice through which the blood flowed from SC to IC (video 3). Unrestrictive cor triatriatum was diagnosed and a cardiac MRI ruled out associated congenital heart defects (figure 1D). Finally, an exercise stress test was normal, so further management was expectant. Three years later, the patient remains asymptomatic. In classic cor triatriatum, a fibromuscular diaphragm with fenestrations divides LA into SC (receiving pulmonary venous flow) and IC (true LA, containing the left atrial appendage and mitral orifice). The insertion of the diaphragm proximal to the left atrial appendage is the feature that