BACKGROUND: Research has shown that decreased heart rate variability (HRV) is independently associated with increased mortality after acute myocardial infarction. However, the relationship between HRV and myocardial ischemia still remains controversial. The purposes of this study were (1) to determine the relationship between HRV and atherosclerosis of the coronary artery; and (2) to determine the relationship between HRV and the extent of coronary stenosis in patients with stressed myocardial ischemia. METHODS: Forty-six patients, 41 males and 5 females, were included in this study. Ages ranged from 50 years to 79 years. Seventeen volunteers served as the control group, which was comprised of 15 males and 2 females of ages ranging from 40 years to 74 years. For each patient a left ventriculogram and a coronary angiogram were performed. According to their coronary angiograms, patients were divided into normal coronary artery group, atherosclerotic coronary artery group and significant coronary artery disease group. An ambulatory EKG was performed on each patient and volunteer. Heart rate variability was defined as SDNN, SDANN, rMSSD, and pNN50 in time domain measures; and low and high frequency in frequency domain measures. RESULTS: There were no significant differences in all variables of heart rate variability between the atherosclerotic coronary artery group and normal coronary artery group. In addition, there were no significant differences in all variables between the significant coronary artery disease group and the control group or between the significant coronary artery disease group and the normal coronary artery group. CONCLUSIONS: These studies have shown that atherosclerotic or significant coronary artery disease with stressed myocardial ischemia does not impair 24-hour heart rate variability.