Abstract: ［Abstract］〓Objective〖HTSS〗〓To investigate the heart rate variability of acute myocardial infarction and unstable angina in acute coronary syndrome, and to clarify the autonomic nerve change rule, so as to provide reference value and new treatment strategy for further observation and treatment and guidance of prognosis.
〖HTH〗〖WTHZ〗Methods〖HTSS〗〓Patients with acute coronary syndrome were divided into acute myocardial infarction group(group A, 32 cases) and unstable angina pectoris group(group B, 47 cases) according to clinical classification.
〖HTH〗〖WTHZ〗Results〖HTSS〗〓Standard deviations of normaltonormal RR intervals（SDNN）, standard deviation of the average normaltonormal intervals（SDANN） and root mean square of successive differece（RMSSD） of group A were significantly lower than that of group B, with statistically significant difference(P＜005), while proportion of number of pairs of adjacent normaltonormal intervals by more than 50 ms（pNN50） of 2 groups showed no statistically significant difference(P＞005).
〖HTH〗〖WTHZ〗Conclusion〖HTSS〗〓In acute coronary syndrome, the autonomic nervous function of the acute myocardial infarction group is more seriously impaired than that of the unstable angina group. The autonomic nervous function of the patients should be actively improved according to the changes in heart rate variability, so as to reduce the incidence of coronary heart disease complications and improve the prognosis of patients with coronary heart disease.

Key words: acute coronary syndrome, heart rate variability, electrocardiography