Heart of Fire

A little bit of Fire Elemental essence. Used in many crafting recipes and a couple of quests.

Heart of Fire as a quest item
Heart of Fire is needed for the following quests:
 * (Alliance)
 * (Horde)

Heart of Fire as an ingredient
Heart of Fire is used in the following recipes:

Alchemy

 * Transmute: Elemental Fire

Blacksmithing

 * Blazing Rapier
 * Dark Iron Mail
 * Dark Iron Plate
 * Dark Iron Pulverizer
 * Dark Iron Shoulders
 * Dark Iron Sunderer
 * Ornate Mithril Breastplate
 * Radiant Belt
 * Radiant Boots
 * Radiant Breastplate
 * Radiant Circlet
 * Radiant Gloves
 * Radiant Leggings
 * Volcanic Hammer

Engineering

 * Dimensional Ripper - Everlook
 * Mithril Mechanical Dragonling
 * Pet Bombling

Leatherworking

 * Helm of Fire
 * Dragonstrike Leggings

Tailoring

 * Cindercloth Boots
 * Cindercloth Gloves
 * Cindercloth Robe
 * Cindercloth Vest
 * Cloak of Fire

Enchanting

 * Enchant Cloak - Greater Resistance