Measurement of heart rate and oxygen uptake during incremental exercise and at maximal exercise is useful in evaluating mechanisms responsible for exercise limitation in patients with cardiopulmonary disease. Presently used prediction equations are based on relatively small groups of subjects in whom there was an uneven distribution of subjects with regard to age and sex or based on equations that were from extrapolated data. Our prediction equations are based on data from 231 men and women equally divided within decades between 20 and 80 years. Patients exercised to a symptom-limited maximum on a cycle ergometer while measurements of heart rate and oxygen uptake were recorded. The relationship between heart rate and oxygen uptake throughout exercise (HR:VO2) was determined using a statistical technique that included each data point from each subject. The HR:VO2 throughout incremental exercise was best described by separate equations for women younger than 50 years and older than 50 years and for men younger than 70 years and older than 70 years. Prediction equations for maximal heart rate (HRmax) and maximal oxygen uptake (VO2max) were developed by linear regression and were selected from all possible combinations of parameters. The HRmax was most accurately predicted by age alone for both sexes. Unlike the HR:VO2 relationship, the slope of the line relating heart rate to age was not different for the older women compared with the younger women so that a single equation was derived to predict HRmax. A single equation for the men was also sufficient since the slope of heart rate to age was the same for all ages. To most accurately predict VO2max, a separate equation was required for both the women and men that included age, height, and weight.