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The purpose of this study was to determine and compare the thermoregulatory and hemodynamic responses to moderate intensity exercise (60% of peak oxygen consumption [O2peak]) in warm (35°C, 45% relative humidity) and cool (18°C, 65% relative humidity) environments in men who had previously undergone coronary artery bypass graft (CABG) surgery and healthy control subjects, matched for age and body composition.Fourteen post-CABG men and 16 healthy control subjects were recruited and walked 40 minutes at a moderate intensity, in randomized order, in warm and cool environments (on separate days). Measures of heart rate, systolic and diastolic blood pressures, rating of perceived exertion, core (rectal)(Tc) and mean skin temperatures (sk), oxygen consumption (O2peak), sweat rate, and blood lactate were taken.Both groups showed a larger increase (P < .05) in Tc and rate-pressure product during exercise in the warm compared with the cool environment. However, Tc and rate pressure product were significantly lower (P < .05), and systolic blood pressure decreased slightly with exercise duration (P < .05) in the CABG group compared with the control group in the warm environment. Heart rate, sk, percent O2peak, blood lactate, sweat rate, and rating of perceived exertion did not differ significantly between the groups in either climate and no subject had ischemia or arrhythmia during test procedures.These results indicate that clinically stable men with revascularized coronary artery disease are able to cope as well as healthy controls with the thermoregulatory and cardiovascular demands of 40 minutes of moderate intensity exercise in warm and cool environments.