Human experience...not canine
, but I had a child born with an ASD (2 holes, actually), and a grandchild born with an ASD. An Echocardiagram should show what the issue is, but will likely be a bit pricey and a specialty. Since this is a puppy mill seizure rescue, you may be able to find a Good Samaritan hopefully that is willing to help. Once the 'cause' is known, the next steps that need to be taken should be easier to formulate I would think. Good luck, and thank you for helping these little sweeties!