The aging process predisposes man to a greater con cern for and sensitivity to his health and fitness. Regular exercise can improve and maintain an individual's gen eral health regardless of the fitness level at the onset of the exercise regimen. We have noted that age does not significantly reduce the benefits (trainability) at tained from exercise; however, it does appear that a prolonged sedentary lifestyle will diminish the fitness level that can be achieved. Cardiopulmonary fitness is primarily a function of the oxygen transport system and, therefore, is monitored by determining maximal aerobic capacity (VO2max). The VO2max is a highly reproducible parameter related to cardiac output and the arteriovenous oxygen differ ence. Exercise conditioning can improve the VO2max by augmenting both the cardiac output and the oxygen extraction within the capillaries. Resting stroke volume is increased by a conditioning effect and resting brady cardia is common. Changes in total peripheral resist ance (TPR) and blood pressure are not as readily demonstrable. To produce a conditioning effect and maintain fitness it is recommended that dynamic exer cise at intensities of 60 to 90% of the maximum heart rate reserve for at least 15 minutes should be per formed at least 3 days/week. The total work load (as a function of intensity and duration) appears to be the most important criterion for producing a conditioning effect. Proper testing and evaluation is necessary for a clinician in prescribing an exercise program that is safe and effective. With the middle-aged individual precau tions must be taken to discern any risks for a cardio vascular event or structural injury.