I think you would have many other symptoms, as well, if it were heart related pain.
I, too, have had an aching left arm for the past few days that has me a little concerned, too. I have a tender spot in my upper back and shoulder as well as a tender spot in my upper left chest. I think they are all related but I still worry about it being my heart.
Try taking a hot shower as someone suggested or a hot bath. A heating pad might also help. Hope you feel better.