[DougG]

If MP or CO had an overpair or TTT, I'd expect to see a raise somewhere -- given that two hearts fell on the flop, I doubt they'd let everyone continue to draw for free.

Looks like MP could have an underpair, a flush draw, A-x, or KQ. Hmm - hard to imagine what CO could have, cold calling a 3-bet preflop, then calling flop and turn. AK/AQ/KQs? TT being slowplayed? 99 or JJ? Some completely random weird hand?

I'm not sure that an underpair calls once the A falls and a missed flush/straight draw almost certainly doesn't, but maybe they'd bet and try to steal the pot? So, check and call if one bets / one checks or folds, hoping to lose this pot only 90% of the time.