Transpositional venous anomalies are common in animals with transpositional arterial anomalies such as PRAA.  The most frequent one is persistent left cranial vena cava (CVC), which is a remnant of the embryonic left cranial cardinal vein and is normal in many species.  It returns blood to the right atrium via the coronary sinus and should not be ligated.  A left CVC crosses over and may obscure the ligamentum arteriosum.  The size of a left CVC is inversely proportional to the size of a co-existent right CVC.  When large, the left CVC must be isolated and retracted to expose the ligamentum.