Patent ductus arteriosus (PDA) is one of the most common congenital heart disorders in dogs. If thecondition is not corrected, more than half of the affected dogs die within their first year of life. Closureof the PDA by occlusion or ligation is therefore recommended and has a good long-term prognosis. Themain complication of the non-invasive techniques is embolism, whereas bleeding after rupture of theductus or an adjacent blood vessel is the most common problem with ligation.Two cases of PDA are discussed. In the first dog, the PDA was successfully corrected surgically. Inthe second case, however, serious bleeding occurred at several occasions during the surgery due to theexceptional presence of a persistent fifth aortic arch (PFAA). Intraoperative euthanasia was performed.