Complete the Heroic Difficulty raid achievements listed below.

Kill Maexxna in Naxxramas within 20 minutes of Anub'Rekhan's death on Heroic Difficulty.

Defeat the bosses of The Military Quarter of Naxxramas on Heroic Difficulty.

With all three Twilight Drakes still alive, engage and defeat Sartharion the Onyx Guardian on Heroic Difficulty.

Defeat Sartharion the Onyx Guardian and the Twilight Drakes on Heroic Difficulty with fewer than 21.

Defeat Sapphiron on Heroic Difficulty in Naxxramas.

Defeat Thaddius in Naxxramas on Heroic Difficulty with less than 21 people.

Kill Patchwerk in Naxxramas in 3 minutes or less on Heroic Difficulty.

Defeat Loatheb in Naxxramas on Heroic Difficulty without killing any spores.

Defeat the bosses of The Arachnid Quarter of Naxxramas on Heroic Difficulty.

Defeat Heigan the Unclean in Naxxramas on Heroic Difficulty without anyone in the raid dying.