At 85 kgs., or 187 lbs., Sampson weighs twice as much as he should.
But the black Labrador from Australia, who has high blood pressure and fatty tissue around his head because of his condition, is too obese to be exercised.
Describing Sampson to be "the size of a small heifer," a shelter worker who helps weigh him has said that the hefty pooch was fed too much of the wrong food.
"His former owners obviously couldn't resist his big brown eyes that follow you around saying, 'Feed me,'" Amber Lavery of Animal Aid told Australia's Herald Sun
Sampson faces tough challenges in trying to reach a healthy weight. He has a big appetite and will do what he can to get more food. Animal Aid hopes that he will lose half his weight by the end of this year, but it will be hard work for everyone involved.
"Tough love means saying no," Lavery said.