I'm not saying there is only one major line with TVD but I hear talk about a popular line that I love and my sources are trying to scare me in another direction.
Fine to say call and ask the producers/owners of dogs in a questionable pedigree, but the reality is that they can be sketchy; after all, no one wants THEIR dog to be the one to blame. I found this particularly true with older, established kennels and breeders.
Years back,I once had a pup with a heart defect (not TVD, but research in other breeds shows it to be genetic) and when I contacted breeders about dogs back in the pedigree (I line breed and didn't want to double up on this particular problem again)I was told basically to keep my mouth shut and mind my own business. "After all", I was told, "you are pretty new to this."
A few years down the road, I found out that some of these breeders had clauses in their contracts with puppy buyers that dealt with puppy replacement should the pup be affected with this heart condition......
So obviously they knew it was present and being produced, but wanting to talk openly about it and where they thought it was stemming from? Not so much.
I find that newer kennels are more forthcoming about things that show up in the lines they work with; this is how it should be to improve problems in our breed.