There may be several causes as to why your shoulder hurts during a chest exercise including dysfunction of the rotator cuff (small muscles that help support your shoulder), other ligaments, tendons, or bursa (fluid-like sac) of the shoulder. Whenever you experience pain during an exercise, it is important to stop the exercise immediately and follow treatment guidelines outlined by your physician. Treatment should help relieve the pain and help restore normal shoulder function. Pain relief strategies may include undergoing a period of active rest (you should move your shoulder, but you shouldn't do strenuous activities like lifting heavy weights), applying ice within the first 24 hours to help reduce inflammation, and taking over the counter anti-inflammatory medicine such as ibuprofen. Once you have been given the clearance to resume exercise, it will be important to incorporate some stretching and strengthening exercises for the shoulder. Some common exercises for shoulder dysfunction include foam rolling for the lats and mid back; static stretches for the chest, lats, and posterior shoulder; and strengthening exercises for the rotator cuff such as a standing cable external rotation.