Flash Heal is a level 10 Holy priest's fast single-target healing spell. It sacrifices mana efficiency in order to land a heal faster on someone who might not live to receive a spell with a longer cast time. The stated design intent for Flash Heal is as a quick but expensive stabilization heal, as opposed to the slower but more potent [Heal].
Flash Heal excels in situations where speed, not mana efficiency, is the prime concern. Conversely, due to its poor mana efficiency, it is best used only in these situations. Wherever possible, more efficient options such as [Heal] are preferable.
Spamming Flash Heal makes for extremely potent healing, but drains mana at an alarming rate.
The spell has a higher single target throughput than [Binding Heal], but if you are hurt, it is generally a good idea to use Binding Heal instead of Flash Heal.
Holy priests can use Flash Heal to reduce the cooldown on [[Holy Word: Serenity].
Hotfix (2013-09-24):Flash Heal now should correctly receive an increased critical chance from Inner Focus while Surge of Light is active.
Patch 5.2.0(2013-03-05): Amount of healing done reduced by 20%. However, the re-introduction of [Spiritual Healing] means that for Discipline and Holy priests, there is no decrease to the amount of healing done.