Post-stroke shoulder pain is defined as pain in the shoulder area that starts after a person has had a stroke. The SPR System is an investigational device that is being studied for the relief of post-stroke shoulder pain. The SPR System uses electrical stimulation and includes a Trial Stage (where a temporary system is used to see if the subject may benefit from this type of therapy) and may include an Implant Stage (where a small device is implanted under the skin in the chest). The SPR System delivers mild electrical stimulation to the muscles in the shoulder where the subject feels pain. This research study will evaluate the effect of electrical stimulation on shoulder pain.