I had breast cancer in June 2011. I have tried taking all three drugs, aromasin,arimades adn femara. Now I have started taking Tamoxifen, 20 mgs. I have fibromyalgia and osteoarthritis. I had such aevere pain on the first three drugs that I am now trying tamoxifen. Today after two weeks on it, I am having chest pain that radiates down my left arm and pain in my shoulder blade. It comes and goes. I do not have any shortness of breath, but I have recently been diagnosed with pvcs. Do I need to be concerned that it is my heart? I know that this medicine can have painful chest pain and shoulder pain as a side effext. I have been seimming 10-15 laps 3 times a week with no shortness of breath. It feels like a pulled muscle.