Chronic dehydration (DEH) and heat stress combined with poor cardiovascular (CV) health may influence physiological responses to exercise. We examined the effects of free-living induced hypo-hydration on physiological responses to exercise in a heated environment and whether resting CV health is related to these changes. Participants (N = 16, 20.6 +/- 1.2 years) were randomized to 3 days of voluntary fluid restriction (DEH) or intake (hydration [HYD]) followed by an exercise bout. CV health was assessed by flow-mediated dilation (FMD), pulse wave analysis, and heart rate variability (HRV). HYD was assessed by weight, urine color, and specific gravity (USG). Exercise trials were conducted in a heated environment (30.3 +/- 0.8 degrees C, 27.4 +/- 7.4% RH) on a cycle ergometer for 30 min. Heart rate (HR), weighted skin (T(sk) ) and mean body temperature (T(b) ) and skin blood flow (SBF) were assessed during exercise. Pre-exercise weight (P < 0.005), urine color, and USG (P < 0.001) were different in between trials. HR was greater in DEH (153 +/- 26 bpm) versus HYD (144 +/- 23 bpm, P = 0.02) after exercise. No group differences were found, but a time interaction P < 0.001) for all temperature responses and time-by-trial interaction for T(re) (P < 0.01) and T(sk) (P < 0.001) was observed. Greater changes in T(re) (P = 0.02) and T(sk) (P < 0.01) were associated with increased FMD. Free-living, continuous DEH alters weight, blood, and urine markers of HYD as well as HR response during exercise. Resting CV health was related to increased change in T(re) and T(sk) , suggesting CV health plays a role in the mechanism of heat dissipation when DEH even in college-age men and women.