Background-Clinical observations suggest that tolerance to heat stress may be impaired in patients with cardiovascular diseases, particularly those associated with impaired ventricular function and congestive heart failure(CHF). However, thermoregulatory function during a controlled heat stress challenge in patients with CHF has not been studied. Methods and Results -To test the hypothesis that thermoregulatory responses are attenuated in such patients, we assessed cutaneous vasodilation and sweat rate in patients with stable class II-III CHF and in matched healthy subjects during passive whole-body heating. Whole-body heating induced a similar increase in internal temperature(≈ 0.85° C) in both groups. The sweating responses in patients with CHF were not significantly different from that in control subjects. In contrast, the elevation in forearm cutaneous vascular conductance in patients with CHF was reduced by nearly 50% relative to the control subjects(3.8± 0.8 versus 6.9± 1.0 mL/100 mL tissue per minute per 100 mm Hg, P=0.04). Moreover, maximal cutaneous vasodilator capacity to direct local heating in patients with CHF was also significantly lower than in control subjects, suggesting that vascular remodeling may be limiting cutaneous vasodilation during hyperthermia. Conclusions -These observations suggest that patients with CHF exhibit attenuated cutaneous vasodilator responses to both whole-body and local heating, whereas sweating responses are preserved. Attenuated cutaneous vasodilation may be a potential mechanism for heat intolerance in patients with CHF. Background-Clinical observations suggest that tolerance to heat stress may be impaired in patients with cardiovascular diseases, particularly those associated with impaired ventricular function and congestive heart failure (CHF). However, thermoregulatory function during a controlled heat stress challenge in patients with CHF has not been studied. Methods and Results-To test the hypothesis that thermoregulatory responses are attenuated in such patients, we assessed cutaneous vasodilation and sweat rate in patients with stable class II-III CHF and in matched healthy subjects during passive whole-body heating. Whole- In contrast, the elevation in forearm cutaneous vascular conductance in patients with CHF (≈ 0.85 ° C) in both groups. The sweating responses in patients with CHF were not significantly different from that in control subjects. was reduced by nearly 50% relative to the control subjects (3.8 ± 0.8 versus 6.9 ± 1.0 mL / 100 mL tissue per minute per 100 mm Hg, P = 0.04). Moreover, maximal cutaneous vasodilator capacity to direct local heating in patients with CHF was also significantly lower than in control subjects, suggesting that vascular remodeling may be limiting cutaneous vasodilation during Hyperthermia. Conclusions-These observations suggest that patients with CHF exhibit attenuated cutaneous vasodilator responses to both whole-body and local heating, while sweating responses are preserved. Attenuated cutaneous vasodilation may be a potential mechanism for heat intolerance in patients with CHF.