To investigate the associtation of heart rate variability with myocardial ischemia we observed the 24 h dynamic electrocardiogram in 35 cases of coronary heart disease. Heart rate variability was obtained statistically by a measure of the standard deviation of the set of all R-R intervals in a 24 h period while myocardial ischemia was estimated by the total time of the myocardial ischemia attack recorded in the 24 h dynamic electrocardiogram. The 35 patients were divided into high and low standard deviation group (high group standard deviation>50 ms ,low standard deviation≤50ms). 22 patients were in high group and 13 patients were in low group. Comparison was made between the 2 groups in the number of transient myocardial ischemia attack and the total time of the myocardial ischemia in a 24 h period. The study showed significant differences existed between the 2 group both in numbers and in the total time of transient myocardial ischemic attack (p<0. 01,p<0.05). Negative correlation of low degree was observed between heart rate variability and total ischemic time (r=-0.29 , p<0. 05 ). Significant difference could also be seen between the 2 groups in the numbers of nonsustained ventricular tachycardia (p<0. 05). Our study indicated that low heart rate variability associated with myocardial ischemia and might be predisposed to serious arrhythmia.