This study was undertaken to elucidate the relationships among cardiovascular drift (CVD),changes in cardiac functions which were observed during prolonged exercise, and aerobic capacity of subjects. Six male distance runners, five male joggers and five male untrained subjects performed 40-min exercise with work load requiring 50% and 65% of maximal oxygen consumption on a bicycle ergometer. Heart rate, stroke volume, blood pressure, systolic time intervals (STIs) and diastolic time (DT) were calculated from electrocardiogram, phonocardiogram, derivative of ear densitogram, impedance cardiogram and finger arterial pressure wave. 1) The higher the aerobic capacity of subjects, the slighter the CVD during prolonged exercise was. 2) Significant negative correlations were found between the aerobic capacity of subjects and changes in STIs and DT during 50% exercise. However, these relationships were not observed during 65% exercise. 3) During 50% exercise, the higher the aerobic capacity of subjects, the later a trough was formed in the ratio of systolic time to DT (QS_2/DT) and the smaller the change in QS_2/DT after the trough was. These findings suggest that the changes in STIs and DT during prolonged exercise depend on the aerobic capacity of the subjects. It is also sugested that myocardial contractility may be more depressed in the subjects with lower aerobic capacity during prolonged exercise.