[DDH]

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This guy has been pretty tight heads up. He either min raises when first to act, or just folds.

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What have you done to his min-raises? Have you come over the top of him on a lot of them, or just checked like you did here? If you'd been checking a lot, to me, this could indicate, not a monster, but that's he's decided he can complete and see a flop with a weaker hand. If you've come over the top of him a lot, then you might have something to worry about.

I probably put him all-in preflop. Or at the very least, I'll bet out when the ace hits. The only reasoning I can think of to check the flop when you hit the ace is to check raise, and heads up, against a tight player, I don't like the play so much, just bet out and push him with your top pair.