To compare the similarity and difference of heart rate variability (HRV) between X syndrome (XS) patients and coronary heart disease (CHD) patients, and to probe for clinical significance of autonomic influnce in patients with XS, the parameters of time and power spectral were measured in 12 XS patients and 12 CHD patients, 12 normal subjects were used as controls. The HRV parameters of XS were analyzed in contrast to group CHD and group normal controls.The results showed that parameters of each time domain in group XS and group CHD are lower than those of control group, RMSSD during night (21:30pm～6:00am) and LF/HF in morning (6:00～6:05am) show significant difference between group XS and group CHD ( P