Abnormal signal-averaged electrocardiography (SAECG) reflects slow and heterogeneous myocardial conduction, predicting ventricular arrhythmia and sudden cardiac death in patients with ischemic heart disease. The purpose of this study was to investigate the quantitative effect of coronary artery bypass grafting (CABG) on SAECG, which is still controversial, and to identify the factors that are related to it. Pre- and postoperative SAECGs were recorded in 100 patients who underwent CABG. Compared parameters included filtered QRS duration (dQRS), root mean square voltage in the terminal 40 ms of the QRS complex (RMS40), and duration of the terminal low-amplitude signal less than 40 microV (LAS40). All 3 parameters in SAECG improved significantly after CABG (dQRS: 105+/-21 ms-->99+/-18 ms, RMS40: 55+/-45 microV-->65+/-41 microV, LAS40: 29+/-19 ms-->25+/-12 ms). The improvements in SAECG were greater in patients who underwent complete revascularization and in those without prior myocardial infarction. In conclusion, CABG improved SAECG quantitatively, even in patients with normal SAECG. However, this improving effect was variable and closely related to the presence of prior myocardial infarction and the completeness of revascularization.