The ability to prescribe exercise for both normal persons and patients with heart disease has advanced from an art to a science during the past decade. Research during this period has given the physician and the exercise physiologist the capability of designing exercise programs to meet a specific person's individual needs, interests and capacity. In such programs, participants first undergo a thorough medical evaluation, including a detailed personal health and family history, physical examination, a resting 12 lead electrocardiogram and an exercise electrocardiogram. Either as part of the exercise electrocardiographic evaluation or as a separate exercise test, individual work capacity (either actual or estimated maximal oxygen uptake) and the maximal heart rate are determined. In the actual exercise prescription, attention is given to four factors: (1) type of activity, (2) frequency of participation, (3) duration of each exercise period, and (4) intensity of the effort. To promote and maintain basic cardiorespiratory health and endurance, the exercise must be of an endurance nature—walk-jog-run, hiking, swimming or bicycling. It should be performed at least three times a week for 20 to 30 minutes at each session. Significant changes in work capacity and cardiovascular function occur when a person exercises at a level as low as 60 percent of his working capacity. A level of 60 to 75 percent is normally used to initiate an exercise prescription. This level can be easily monitored by the participant, using 60 to 75 percent of his maximal heart rate as the guide for his training or exercising heart rate. In all cases, the exercise is programmed to fit the individual subject, not vice versa, as often happens in group programs. This approach provides a safe and efficient means for assisting adults to gain maximal benefit from exercise.