Although cigarette smoking is known to be a strong risk factor for the development of coronary artery disease, several large clinical studies have demonstrated that current smokers had a favorable prognosis compared to nonsmokers after myocardial infarction. This study sought to evaluate the effect of smoking status on heart rate variability after onset of acute myocardial infarction. We studied 52 patients (34 smokers, 18 nonsmokers) with a first myocardial infarction within 24 h of onset. We recorded 24-h ambulatory ECG to calculate very low frequency power (VLF), low frequency power (LF) and high frequency power (HF) 14 days after onset. Although smokers had a tendency to be younger than nonsmokers (mean age 57 versus 62, P = 0.0812), clinical characteristics were not statistically different between smokers and nonsmokers. After adjustment for age, left ventricular ejection fraction, history of diabetes, acute revascularization and use of beta-blockers, VLF (P = 0.0183) of smokers 14 days after onset was significantly higher than for nonsmokers. In conclusion, although smoking reduces heart rate variability in the general population, higher heart rate variability was observed in smokers than nonsmokers after acute myocardial infarction under the condition of smoking cessation.