The elevated CO2 levels, elevated temperature, and lower blood pH that may occur during exercise should enhance O2 delivery to the exercising muscles. It was hypothesized that performance of prior exercise (PE) would result in a faster VO2 response, as well as a reduced slow component contribution, in subsequent exercise bouts. Five women (21 ± 1 yr) and 10 men (23 ± 2 yr) performed nine 6-min bouts of heavy intensity cycle ergometer exercise (i.e., above the ventilatory threshold, individually determined by an incremental test). Three bouts were performed without prior heavy exercise (noPE), three were performed 6 min after a 6-min bout of heavy intensity arm cranking (PEA), and three were performed 6 min after a 6-min bout of heavy intensity cycle ergometer exercise (PEL). Breath-by-breath VO2 data from each of the three sets of three tests were combined and fitted to a two-component model, which ignores the cardiodynamic phase. The primary and slow component amplitudes were truncated to reflect actual increases in VO2 in each phase. The effects of PE on the time constant of the primary component were inconsistent. As hypothesized, the amplitude of the slow component was reduced by PE (noPE vs PEA vs. PEL: 25% …