You shouldn't really be pulling aggro that easily with a few cures. I've been on runs where it feels like everything i do pulls something. It's just sometimes more to do with inexperience of the Tank than yourself. Of course if you are not timing your heals or you have regen up when adds spawn the Tank can't be blamed for that. But i've seen a few who think that using a provoke at the start then just DPS'ing is enough to hold aggro from everything. The difference between a poor to average Tank and a good Tank is that the good one can tell instantly they have lost aggro and you have to go out your way to pull from them with a chain of heavy heals.