In November 1989, Guiness Book of World Records recognized a Mastiff from England named Zorba as the heaviest dog in the world, at over 343 pounds.
Zorba stood 37 inches at the shoulder and was 8 feet 3 inches from the tip of his nose to the tip of his tail. He set the Guiness Book record when he was 8 years old, and about the size of a donkey.
Another huge contender was a Saint Bernard named Benedictine. His weight was provided, not by direct measurement, but by “successive studies”, and his weight is reported to be between 336 and 357 pounds.