We studied heart rate variability in 14 healthy women before and after oophorectomy compared with 14 matched women who underwent hysterectomy with ovarian conservation. Surgical menopause induced a decline in cardiac vagal modulation with a shift toward sympathetic hyperactivity. Recovery of the baseline condition after 3 months of estrogen replacement therapy in oophorectomized women suggests a role of estrogen in the autonomic nervous control of the cardiovascular system.