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.

Angiocardiogram and necropsy photograph of a large persistent left cranial vena cava (L) in a dog with PRAA and absent right CVC. The LCVC carries blood to the coronary sinus (CS), right atrium (RA), right ventricle (RV), and pulmonary artery (P).

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A left cranial vena cava is extrapericardial where it crosses over the ligamentum or ductus. The LCVC can be easily isolated and retracted dorsally or ventrally as in this dog with a PDA.

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Necropsy photograph of both persistent left CVC (L) and hemiazygos vein (H) in a dog with retroesophageal right subclavian artery (not visible in photograph).

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Surgery photograph of a dog with PRAA and left hemiazygos vein (H). This vein is a remnant of the left supracardinal system but does not usually obscure the ligamentum if there is not a left CVC.

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