The only time Heathcliff used a cheat was in the first match against Kiritard, where he stopped time.

His shield is moved by himself. He just went out of his way to memorize the attack patterns of all the sword skills in the game, which means that you have to fight him with ACTUAL skills, instead of being guided by the system. Note how, in the animu, the only time he used a sword skill was as a finisher after Kirito blew his own sword skill in that final fight.

The only really cheap thing he has is the OP durability of his shield, but then again, Kirito has the two strongest swords in the game.