The cardiac autonomic nervous activity（CANA）and its circadian rhythm were investigated by frenquency and time domain measures of heart rate variability（HRV）in 30 patients with unstable angina pectoris（UAP group）

22 with stable angina pectoris（SAP group）and 20 control subjects.The results showed that the index of HRV were all significantly lower（P

<

0.001）in UAP group and its circadian variation was markedly smaller compared with SAP and control groups.In the early morning

LF、HF、HF

NU

decreased quickly with an sigificantly increase in LF

NU

、LF/HF（P

<

0.01）.Patients in UAP subgroup with serious cihnical state had lower HRV than patients with mild symptoms

after treatment

HRV were partially restored.The study suggests that CANA are impaired especially vagal activity in UAP group

the sympathetic activity are relatively overactive.In serious UAP group

the CANA are impaired severely.In UAP group

CANA still have a ciradian rhythm

but less variation.In the early morning

the vagal hyperactivity transformed to sympathetic hyperactivity

which may trigger the peak occurence of acute cardiovascular events.Therefore

the abnormal CANA may be as a significant predictor of the patent’s clinical state.