I healed my first heroic in LFD, a big difference from healing normal 5 mans. Halls of Origination was not easy to heal in normal, on heroic I was poping Divine Hymn on every other boss. I oomed for the first time...when we were downing Rajh.
It's expecially tough when you don't get time to mana up after every boss. Toons got one shotted a couple of times. It was quite stressful. This is my first healer, leveled up holy 20-85 healing in LFD this month.
I thought I was doing pretty well healing but this was a wake up call, maybe holy is not for me... I usually try to run over geared but that has been harder to do since I hit 85. I haven't even tried a raid yet and I'm nervous to try another heroic 5 man.