I went through a period of a similar thing, although perhaps not quite as intense. It seems to have eased now, but strangely, the pain that used to be almost exclusiely on the left have now spread to the otherside. I rarely get heartburn with it, although I do get quite gassy. The main similarity is that my discomfort was pretty much constant for about a week.
I'm new to all this and by no means an expert, but I'd say if in doubt get it looked at however, I've heard plenty of other people talking about similar symptoms, often to the point they get sent to casualty (ER) and then it still turns out to be GERD.
For me, I saw a doctor who reassured me it was just acid reflux and then I was more or less happy (despite being a bit of a hypochondriac!!) I've since got back into cycling and put quite a lot of stress on my heart without any problems, so I have to conceed he was right.
Hope everything turns out OK.