Remember to listen to your body. If you start to feel dizzy, faint or nauseous, stop your workout immediately. This is not the time for fitness bravado; pushing yourself to extremes. Leave that for some other time when potentially life-threatening side effects are not involved. In fact, if you know you're not acclimatized to the heat yet and the temps spike into the 90's, you may want to consider bringing your exercise indoors—especially if you're doing high intensity exercises.