Previous studies have shown that the kinetics of heart rate (HR) recovery are delayed in older individuals after exercise. This study was designed to determine whether this observation held when the variables of physical fitness and work intensity were controlled. Twenty male subjects were categorized into four groups (n = 5) according to age and fitness level (peak O2 consumption ml. kg-1.min-1): young trained (YT) 24 +/- 2 yr, 63 +/- 3 ml.kg-1. min-1; old trained (OT) 51 +/- 2 yr, 57 +/- 3 ml.kg-1.min-1; young untrained (YU) 25 +/- 3 yr, 44 +/- 2 ml.kg-1.min-1; old untrained (OU) 57 +/- 4 yr, 36 +/- 4 ml.kg-1.min-1. Bicycle ergometry exercise was performed in incremental stages to a maximally tolerated level of exertion, and HR was monitored continuously postexercise. Regression analysis of the fast (15-120 s) and initial slow (120-240 s) phases of recovery showed no effect of age on HR recovery when comparing YT vs. OT and YU vs. OU. Trained subjects, irrespective of age, demonstrated a significantly faster HR recovery than untrained subjects which was particularly marked during fast-phase recovery (P less than 0.005). These results indicate that the slower HR recovery previously reported in older subjects may be due to a failure to control for variables that influence recovery HR.