Purpose:The purpose of this study was to examine the effects of heat exposure on heart rate and VO₂during a time to exhaustion (TTE) exercise bout. Methods:Eleven college-age men completed 3 experimental trials: a VO₂max test and cycling trials at 90% VO₂max in 22°C (MT) and 35°C (HT). The TTE exercise followed a 60-minute steady state at 60% VO₂max and continued until volitional fatigue. Heart rate and VO₂were measured continuously during the TTE. PRE, MID, and POST time points were calculated for each participant based on their individual TTE. Data were analyzed using repeated measures ANOVA. Results:There was a significant interaction for heart rate (F=6.180, p=0.024, h²=0.382). Heart rate increased from PRE to MID to POST for both MT and HT (p<0.001). In addition, heart rate was significantly greater in HT (159.82 +17.47) compared to MT (146.09 +20.70) at PRE (p=0.031). There was also a significant interaction for VO₂(F=4.312, p=0.030, h²=0.324). VO₂also increased from PRE to MID to POST for both MT and HT (p< 0.05). In addition, VO₂was significantly greater in MT (3.30 +0.52) vs HT (3.05 +0.33) at POST (p=0.025). There was a significant difference in TTE between conditions (p=0.008) with MT (303.00 +121.20 seconds) being significantly longer than HT (174.00 +54.41 seconds). Conclusions:This data suggests that the participants were able to perform at a higher intensity and for a longer duration in MT compared to HT.