I have left shoulder blade pain, pain under left breast and pain that goes from the left side of my neck down my left arm.

Ulnar radiculopathy: Muscle spasm or a herniated disc in your neck may be the cause of your pain. Your symptoms are typical of an ulnar radiculopathy. See a physician for an evaluation to rule out other more serious causes of the chest/breast/ left arm discomfort.

PINCHED: nerves in your neck ("Radiculopathy") are probably the "culprits". Sounds like a CERVICAL (Neck) MRI is indicated plus some Physical Therapy...start with your PCP (Primary Care Provider) Hope this is helpful Dr Z

Pinched nerve: Because patients having cardiac problems can have these symptoms, you should have this ruled out. But the most common cause is an irritation of a nerve in the neck by a bone spur or herniation that can cause pain or numbness that runs down the arm into the hand. An MRI can usually show the cause of the problem if it does not resolve. Thank you for the question.