Although there has been considerable attention paid to the prognostic significance of the heart rate rise during exercise, only recently has it been noted that the heart rate fall after exercise, or "heart-rate recovery," may be an even more powerful predictor of outcome. Heart-rate recovery after exercise is a consequence of central reactivation of vagal tone. As impaired parasympathetic function has been associated with increased risk of death, the study tests the hypothesis that an impaired heart-rate recovery is a powerful and independent predictor of mortality.