The purpose of the present investigation was to describe, for a subset of a large random survey of men and women, restricted to the ages of 55 to 85 years, the physiological decay pattern for aerobic fitness and contributing factors of cardiovascular and pulmonary function. The time course of the age-related changes in maximal oxygen uptake (VO2max), ventilatory threshold (TVE), maximal ventilation (VEmax), maximal heart rate (HRmax), and O2 pulse (VO2max/HRmax) were examined by fitting the data to a decaying exponential model by use of a least-squares parameter estimation technique. The time constant (tau) was used to describe the rate of decline. The women showed a much slower decline in VO2max (tau = 47.4 years) and TVE (tau = 83.3 years) than the men (tau = 20.8 and 15.4 years, respectively). There was a significant age-related decrease in body weight (0.45 kg.yr-1) in the men, whereas the women showed no change. Pulmonary function did not limit performance based on the very slow decline in VEmax and the normal FEV1.0. The decay in HRmax was better described by a linear model, resulting in an extremely slow tau. Maximal O2 pulse clearly exhibited an exponential decay, with a shorter tau (tau men = 13.5 years; tau women = 28.5 years) than any other variable.