It may not be heart related. If he's aware of this new development with his heart, he may be upset and stressed. My daughter always seems to have stomach problems whenever she's stressed, always been that way and she's 27 now.
However, if this is a new symptom and he's feeling miserable, at least call his doctor and ask about it. No need to go on feeling so bad when the doctor may be able to calm things down in his tummy.
I'm still that way, and I'm wayyyy past 27 : )
It wouldn't hurt to have the doctor take a look see.