Soon, Kai was put on a strict diet and started water therapy to help strengthen his legs while burning off fat.
Over time, Kai learned that Heggie was trying to help him and that he was going to succeed.
After a few months he was able to walk to the end of the block, could run and was able to jump up and down into Heggie's car.
"It's crazy. It's like raising your child and you look at them and they're all grown up and you just wonder how that happened," Heggie told Good Morning America.
"I look at him and forget how broken he was. Now he's just a regular dog doing regular dog things like everybody else.
"He truly amazes me every day … Everybody has things they need to do – and he was just so happy … every day he was like this is what we have to do and I'm going to do it. And every day he did it.
"He shows you how to do a really big task literally one day at a time," Heggie said.
"He doesn't worry about yesterday, he doesn't worry about tomorrow, he just focuses on what needs to be done today and he does it. We can learn a lot from dogs."