BACKGROUND: In survivors of acute myocardial infarction(ANI), reduced heart rate variability(HRV) has been demonstrated to be an independent predictor of sudden cardiac death and mortality. The heart rate variability can be examined and analyzed non-invasively and quantitated with 24-hour ambulatory ECG monitoring. In general, the patency of infarct-related artery appears to be one of the most important prognostic factor after AMI. Therefor, the correlation between infarct artery patency and HRV was examined in survivors of AMI. METHODS: The 24-Hour ambulatory electrocardiogram was performed in 23 patients with AMI and 20 normal controls, and analyzed for frequency & time domain HRV. HRV was recorded dwithin 7 days after AMI, and coronary angiogram was performed at 7th day after AMI. The AMI patients were divided into two groups, depending upon patency of infarct-related artery and correlated to clinical manifestations. Thirteen patients had patent vessel(Group 1) and ten patients had non-patent vessel(Group 2). Parameters of frequency domain HRV include LF, HF & LF/HF ratio and time domain HRV include SDNN, SDANN, SD, rMSSD and pNN50. RESULTS: All parameters of HRV was depressed in patients of AMI than in normal control(p<0.05). The mean left ventricular ejection fraction(LVEF) was 54.1+/-10.6% in group 1 and 42.6+/-12.2% in group 2(p<0.05). The mean values of LF, SDNN, SDANN, and SD in group 1 and group 2 were 5.09+/-0.83msec2/Hz & 4.09+/-0.53msec2/Hz, 84.5+/-24.2msec & 59.0+/-11.8msec, 73.2+/-22.8msec & 50.5+/-12.6msec, and 37.8+/-13.1msec & 27.2+/-4.4msec(p<0.05), respectively. There was no difference between two groups in HF,rMSSD and pNN50. The location of infarction and thrombolytic therapy itself did not influence of HRV. The mean values of HF, SDANN, rMSSD and pNN50 in patients with LVEF<40% were reduced significantly than in patients with LVEF> or =40%. There was a significant correlation between LVEF and LF, between LVEF and HF and between LVEF and LF/HF ratio(r:0.55, p<0.05;r:0.67, p<0.05;r:-0.56, p<0.05). CONCLUSION: HRV was depressed due to reduced vagal activity in patients with AMI. The values of LF, SDNN, SDANN, and SD in group of patent infarct-related artery were reduced significantly than in non-patent group.