Divine Hymn

Divine Hymn is a priest ability learned at level 78 for. Like the Holy talent ability Circle of Healing it 'smart-heals' by selecting the 3 party or raid members within 40 yards with the lowest health, and channeling a very substantial amount of healing to them over 8 seconds (1 tick every 2 seconds). In addition, it grants a 10% increased healing buff to those targets for 8 seconds.

Known bugs
As a channeled spell, Divine Hymn is treated as a Heal over time, allowing haste to accelerate the rate at which its ticks occur. With sufficient haste, extra ticks are added to a HoT, improving not only its HPS but also its mana efficiency and total amount healed. Divine Hymn should be an exception to this, as its tooltip specifically states a maximum of 12 heals. However as of Patch 4.1.0, Divine Hymn responds normally to haste, with sufficient amounts granting extra ticks and so an increased total amount of healing. By using haste-granting trinkets, racials and spells (such as Power Infusion) before casting Divine Hymn, the priest can dramatically increase the number of ticks and so total healing generated by the spell, particularly useful when used as an emergency heal. Additionally, because Divine Hymn's targets are selected each tick, any extra healing generated will not be wasted as overheals on targets already at full health.