I'm sorry your little guy was diagnosed with a shunt, fortunately with surgery he can live a long healthy life.
You may want to explain how they came up with this diagnosis. Many vets aren't familiar with liver shunt and we can help you in regards to the next steps and testing.
Here's some additional information....
Portosystemic Shunts FAQ
Also a quick search on this site for the phrase liver shunt will bring up loads of threads.