Unexplained shoulder pain that does not change when you move your neck, shoulder, or arm or that occurs with symptoms elsewhere in your body (such as in your abdomen or chest) may be referred shoulder pain. Referred pain means that a problem exists somewhere else in the body other than where you feel the pain.
Heart or blood vessel problems in which pain is more often felt in the left arm and shoulder, such as heart attack or inflammation around the heart (pericarditis).
A lung problem, such as pneumonia, where pain may be felt throughout the shoulder, shoulder blade area, upper chest, upper arm, neck, and armpit. Pain is usually felt in the shoulder on the same side as the lung problem.