Any reason to hesitate calling here?

I don't have the actual hand history... but I will describe to the best of my memory.

I hold 67 suited and limp from mid position. About 4 other limpers and the flop comes K89 rainbow. First position min raises, and i call with my OESD, and so do the rest.

Turn comes 10 of hearts, giving me my straight and putting 2 hearts on the board. First position min raises again and I reraise him about 6 times the bet. He calls. Everyone else folds

The river comes rag of hearts, putting 3 hearts on the board. First position goes all in for his stack which is about the size of the pot. I didn't like to see that thrid heart but I called and won. He had 2 pair.

Should there have been any doubt in my mind as to whether to call this just because of the third heart? Or am just being paranoid?

There was no flush draw on the flop, so him having that is less likely. It's still possible and definitely worth considering, but you came to the right conclusion. Good job.

Did you reraise on the turn about the size of the pot?

I wouldn't worry much about back door flushes with a flop bet. If he stayed in a hand on the flop it's extremely unlikely that he hit a part of it AND has 2 hearts.

g00t call