Kai the golden retriever lost more than 100 pounds after his previous family brought him to a vet to be euthanized (Picture: This is Kai Facebook page)

A golden retriever lost more than 100 pounds after his owner took him to be euthanized by a veterinarian.

Instead, the vet got in touch with animal workers to help the dangerously overweight dog, named Kai, find a new family.

Pam Heggie said she does not know much about Kai’s past, but she knew he needed help.

The veterinarian told Heggie ‘(Kai) is the most overweight animal I’ve ever seen…anything you do is gonna help that dog.’

‘Anything that he will let you do is good for him,’ the vet said to Heggie, who became Kai’s new foster mother and helped him lose more than half of his body weight.

Kai found it incredibly difficult just to walk up his new foster mom’s three front steps when he first got to her home (Picture: This is Kai Facebook)

When Heggie first brought Kai home, it took him 20 minutes just to climb the small set of stairs that led to her front door, Heggie told Good Morning America.

She began taking him for regular walks, three times day, which were difficult at first, but became easier with Kai’s relentless determination.

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Heggie said: ‘Literally, he went five to ten steps, and they would lay down and start panting.’

But Kai began improving bit by bit.

‘We went to the closest neighbor’s driveway and then the next neighbor over,’ Heggie said.

Kai underwent aquatic therapy to help him strengthen his back legs (Picture: This is Kai Facebook Page)

Step by Step, Kai continued to improve his health (Picture: This is Kai Facebook Page)

Kai began a strict diet and even started water therapy to help him strengthen his back legs. Throughout it all, he remained a happy pup and refused to give up.

Heggie said: ‘He learned that I was going to help him and we were going to be ok.’

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Eventually, Kai began showing noticeable signs of improvement. He was able to reach the end of the block. He could hop into her car. He even began running at the park.

‘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 said.

‘I look at him and forget how broken he was. Now he’s just a regular dog doing regular dog things like everybody else.’

On Friday, Kai’s incredibly weight loss was featured on Good Morning America.

‘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.’

Heggie was not the only one shocked by Kai’s weight loss. On Friday, he showed off his inspiring transformation on Good Morning America.

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‘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.’