Is the world's largest dog a wolfhound?

There is no current World's Largest Dog listed in the Guinness Book of Records. However, back in 1989 Zorba, an English Mastiff, tipped the scales at 343lbs and made it into the Guinness Book of Records. The English Mastiff is the largest breed of dog and the Irish Wolfhound the longest. In 2001, Joe Flynn's English Mastiff, Hercules, made the record book for heaviest dog at 282lbs. Gibson is the current longest dog at 8 feet and 3 inches.