Heroic items are upgrades of items that drop in Cataclysm 5-player Heroic mode dungeons, and Wrath of the Lich King (Trial of the Crusader and Icecrown Citadel) and Cataclysm 10-player Heroic mode and 25-player Heroic mode raids. Heroic items have the same name and generally have the same stats, but more of them.
Exceptions would be the heroic versions of items that drop in Deadmines and Shadowfang Keep. Normal mode for those instances is tuned for around level 15, while heroic mode is tuned for level 85. Such a massive level difference means that the heroic versions of the items are quite different from the normal versions.