What breeds are commonly affected with shunts?
Small breed dogs tend to have shunts that form outside of the liver ("extrahepatic"). In the United States, Yorkshire terriers have almost a 36 times greater risk of developing shunts than all other breeds combined. Extrahepatic shunts can be seen in any small breed but are also reported commonly in schnauzers, Maltese, dachshunds, Jack Russell terriers, Shih Tzu, Lhasa apso, Cairn terriers, and poodles. Large breed dogs tend to retain the fetal liver shunt (patent ductus venosus), or "intrahepatic" shunts. In the Netherlands, about 2% of Irish Wolfhounds are born with intrahepatic shunts. Intrahepatic shunts can be seen in any large breed dog and have been reported in some small breed dogs (especially poodles); in the United States, we see them most often in Labrador retrievers. Australian shepherds, Australian cattle dogs, Samoyeds, and Old English sheepdogs are also commonly reported.
http://www.vet.utk.edu/clinical/sacs/shunt/faq.shtml