Priest · Holy · tier 4 · from level 25

Improved Healing

+59.4 Penance healing

3/3 · level 60 · per 100 mana · and 5 more

Improved Healing 123

Rank 3/3

Reduces the Mana cost of your Lesser Heal, Heal, Greater Heal, Penance, and Prayer of Mending spells by 15%.

Penance healing +17.6% +59.4 Greater Heal +17.6% +49.5 Lesser Heal +17.6% +40.4 Heal +17.6% +39.6 Prayer of Mending +17.6% +19.0 Penance +17.6% +12.3

Averages, counting crits and misses, for a level 60 Priest with a typical weapon and no other gear or buffs, against a target your level. Worked out from the game's own data, the same way as the Foresight addon.