Movies and TV often show someone clutching his or her left arm during a heart attack. Pain in one, either or both arms is indeed a sign that you could be having a heart attack. You could also experience pain in one or both shoulders or back. And as with the chest pain, it may feel very mild -- like a tightness, pressure or general discomfort.
Of course, this type of pain could also indicate you're overdoing it in a tennis match. One way to tell that the pain in your shoulder or back is indicating a heart attack is if it's happening in conjunction with chest pain. If your left shoulder starts to ache and your chest hurts, too, by all means call 911 immediately.
It's important, by the way, that you call 911 first, not a family member or friend. Call a friend only after emergency personnel are on their way.
If your back, arm or shoulder hurts and you also have the next symptom on the list, you should get medical attention without thinking twice, no matter your age or state of health or whether your chest hurts.