I probably would have popped the raise to more like $6-7 on the flop. 3-way and lots of draws. I'm guessing MP3 has the shit with that cold call after two reraises.

If MP2 is a donk like you say..could have two pair or an over pair. With the raise you made and MP3 calling, if you want to stay in the hand....

...maybe just call and hope for the boat or push if a heart falls. Course that would work better if you were first to act.