The classic form of cor triatriatum, demonstrating a fibromuscular membrane in the left atrium separating the proximal chamber from the distal chamber containing the mitral valve and left ventricular inflow. Of note, this drawing contains an atrial septal defect which is not required to be present for the diagnosis of cor triatriatum. LV: left ventricle, RV: right ventricle, LA: left atrium, RA: right atrium, MV: mitral valve, ASD: atrial septal defect, PV: pulmonary vein, PC: proximal chamber, and FM: fibromuscular membrane. (J Tehran Heart Cent. 2010 Summer; 5(3): 153–155. Published online 2010 Aug 31. © Copyright Policy: open-access, License.