Pain in the left shoulder could mean several things. According to the Mayo Clinic, causes of pain the left shoulder range from simple sprains and strains to more life-threatening conditions that require immediate medical attention. Common causes for shoulder pain are a torn rotator cuff and tendinitis.
If pain in the left shoulder is accompanied by pain in the chest, it is possible that one could be suffering from a heart attack. Stroke is also a concern with pain in the left shoulder. The Mayo Clinic's Stroke page states that numbness or pain on one side of the body accompanied by slurring words or blurred vision could be signs of a stroke.