Hi Clint, my name is Sarah I've had similar symptoms to this and it happens to me repetitively. I'll stand still until it passes but inevitably it comes and goes constantly. It feels like a stabbing pain that hurts when I breath in. When it passes it leaves more of a popping sound. If you have something similar to this than I wouldn't neccesarily look at heart disease. These sessions have happend to me numerous times a few for 30 minutes but mostly 1-5 minutes. I did some research on it and found it to be Precordial catch syndrome. Which there isn't much known about it seeing as how it comes and goes quickly so it's assumed to be a pinched nerve located on the left side seeming just under the ribs. I'm 15 and have had these problems since 6 it's nothing fatal at least from what little information is said on it. Hope this helps.