I wouldn't wait to take him to the doctor if you're really worried. Because even if it's really nothing, it doesn't hurt to find out. But I think you should really talk to someone who's an expert in the heart field, because pediatricians and family practice docs may not know enough about the problem to diagnose anything.
I have very heavy beats occasionally, like the women in my family, and I got hooked up to a recorder for 3 days with lots of little stickies on my chest connected to cords. I'm not sure it was the most effective way to test my problem but their test came up normal because the beats only happen every so often. My point is that you could have to go through some testing, but the heart is such an important thing. And you really will feel better knowing what is going on. I don't know how expensive it all is, but if you don't do anything and then he has a problem later, the problem could be much more expensive. Good luck.