A 2-month-old Brittany spaniel dog was presented for persistent regurgitation, first observed soon after weaning. Clinical examination and diagnostic imaging suggested megaoesophagus associated with a vascular ring anomaly. The normal location of the trachea on the X-ray was not consistent with a persistent right aortic arch. Postmortem examination revealed a persistent left cranial vena cava that formed a non-elastic fibrous band enclosing the oesophagus and trachea, and causing constriction of the oesophagus. This uncommon congenital vascular defect has never previously been associated with megaoesophagus in the dog.