INTRODUCTION: The prognosis of women with congestive heart failure (CHF) is better than that for men, but the mechanisms underlying the female survival advantage are not well understood. CHF is characterized by profound abnormalities in cardiac autonomic control that contribute to progressive circulatory failure and influence survival. METHODS AND RESULTS: Time- and frequency-domain heart rate variability (HRV) indexes were obtained from 24-hour Holter recordings and compared to assess the role of gender in 131 men and 68 women with CHF (mean age 60 +/- 13.6 years, range 21 to 87; New York Heart Association Functional Class III [66%] and IV [34%]). Gender-related differences in HRV were observed only in the subset of patients with nonischemic heart failure (55 men and 39 women). Among the time-domain indexes, the SD of the RR intervals (76 +/- 5.3 msec vs 55.3 +/- 3.2 msec, P < 0.0001) and indexes denoting parasympathetic modulation, the percentage of RR intervals with >50 msec variation (4.0% +/- 1.0% vs 6.5% +/- 1.3%, P = 0.02), and the square root of mean squared differences of successive RR intervals (19.1 +/- 3.3 vs 28.4 +/- 3.8, P = 0.004) were higher in women. Among the frequency-domain indexes, the total power (7.5 +/- 0.13 ln-msec2 vs 8.3 +/- 0.14 ln-msec2, P = 0.0002), the ultralow-frequency power (7.2 +/- 0.11 ln-msec2 vs 8.0 +/- 0.14 In-msec2, P < 0.0001), the low-frequency power (3.8 +/- 0.25 ln-msec2 vs 4.8 +/- 0.28 ln-msec2, P = 0.006), and the high-frequency power (3.8 +/- 0.24 ln-msec2, vs 4.6 +/- 0.26 ln-msec2, P = 0.003) were greater in women than in men. CONCLUSION: Women with nonischemic CHF have an attenuated sympathetic activation and parasympathetic withdrawal compared with men. Gender-based differences in autonomic responses in the setting of CHF may be related to the female survival advantage.