Pain developed in left shoulder blade/down left arm/4 days ago. now it really hurts down the back of left arm, when i cough. it comes in waves.

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.