Differentiating Shoulder Pain

Hi,
I have had recurring shoulder pain in my left shoulder and between my shoulder blades for a year now. It comes and goes, sometimes worse if I am sleeping on my stomach with my arm tucked under my head. When I shrug my shoulders I feel a pop in my left shoulder blade near my spine. I also feel tenderness in my neck at the junction to my shoulders just above the shoulder blade.

Ok heres my problem.  I recently was admitted to the hospital for Afib.  A stress test showed that I also have some blockage in one of the arteries to my heart. I have been told to watch for any sign of heart pain.  Now I have begun to wonder, could this pain be caused by my heart rather than a shoulder problem.  The feeling is like that of a pinched nerve, or a torn ligament. A sore tearing feeling.  I had always blamed this on my job, which involved some heavy lifting and twisting using ladders. Now I am confused, and worried.  I asked the cardiologist, but he said he couldn't tell me.  It does not seem to be connected with exercise other than twisting or bending.  Walking, etc does not seem to make it any worse. It is more when I am sitting in a chair or laying down at night.