Summary

We present a rather unusual cause for syncope associated with atrial tachycardia. A man aged 39 years presented with an episode of syncope and narrow complex tachycardia. Further investigations, including transoesophageal echocardiography, identified cor triatriatum sinistrum (CTS), a rare congenital abnormality characterised by the atrium being divided by a fibrous membrane. Although it is rare, there has been an increase in diagnosis due to developments in diagnostic imaging techniques. Symptoms are related to the size of fenestrations within the fibrous membrane. Presenting symptoms can mimic those seen in mitral stenosis. It is a condition that can occur in isolation, but it can also be associated with other cardiac abnormalities such as an atrial septal defect (ASD) (as in this case). Surgery is the definitive treatment (this man had surgical repair of CTS and closure of ASD) and should be considered at any age if there are any associated symptoms or complications.