I too have had some of these spasms. However, mine is on the right side so I know it's not my heart. The pain is right below the collar bone but slightly above the breast. It is a very sharp spasm that may last from a couple minutes up to thirty minutes. It quite often will take my breath away.

Is this similar to what you are feeling?

I haven't been to a Dr. since this started so not sure exactly what it is yet, but may be similar to what your experiencing. Usually a hot compress or bath will help mine go away. I also ice the area in the evenings when I am not having spasms. (Don't know if that helps or not, but the area actually feels a little swollen)