Divided left atrium (Cor Triatriatum Sinister) with atresia of the right pulmonary veins in a cat

A nine-month-old, female Maine Coon cat was referred for acute respiratory distress. Echocardiography revealed the presence of a membrane dividing the left atrium into two chambers, suggestive of cortriatriatum sinister (CTS). Due to poor prognosis, the owner elected for humane euthanasia. At necropsy, a transverse fibromuscular membrane containing an orifice dividing the left atrium into two chambers was observed, confirming the diagnosis of CTS, or divided left atrium. Moreover, atresia of the outflow of right pulmonary veins into the left atrium was identified. This study reports the rare instance of CTS associated with anomalies of the pulmonary venous connection.