In my experiences I've noticed most healers like to keep you topped off. For instance you take 500 damage, get healed for 1500. Since only 500 was applied to your life pool you only received 50 mana back(at lvl 70). As counter productive as it seems when healing a pally it is usually better when you are not topped off all the time. If your health fluctuated around 50% - 75% you would be getting the full mana return which makes it a little tougher for healers, and puts you in a position where you could die but hey if you are specced 5/5 Ardent Defender you get a little more breathing room.

Also if you are running Heroics, you might want to use gear with Intelligence and Spell Damage like the D3 of the righteous set or tiered pieces. That usually helps me out. When it's beneficial sometimes I skip my holy shield rotation to take a little more damage(it's not much but its better then nothing) until my health drops a bit then I don't have to worry about oom.

Lastly you should rank down your consecrate and where 2 pieces of D3 to lower the mana cost. Seal Wisdom, pull with shield(or decapitator from prince if you have it) consecrate, judge, and seal righteous. Use that rotation if threat is not an issue.
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