I think it's probably just gas. I've had really, really painful gas sometimes that actually felt like it was pushing upward and felt kind of like what you are describing. Try some gas medication and stay away from excessively rich fiber foods for a while. Like raw veggies and beans, that stuff will cause it to get worse. Or try some Beano, that might help, too.
I don't think it's your heart, I think it's more likely gas. But I'm not a doctor and I'm just guessing.