BACKGROUND: Previous studies have shown that after coronary artery bypass grafting (CABG), heart rate variability (HRV) becomes decreased, even more significantly than in patients after myocardial infarction (MI). According to some reports, unlike in patients after MI, decreased postoperative HRV does not increase mortality in CABG patients. The aim of this study was to compare differences in mortality rate in CABG patients with normal vs. decreased postoperative HRV. METHODS: This study included 206 consecutive patients who underwent CABG. During stationary rehabilitation, 24-hours Holter ECG was performed on all the patients, and HRV was analyzed from its recordings. After leaving cardiac rehabilitation, all patients were contacted in writing to provide data on their health in the follow-up period. In the analysis of survival rate depending on HRV findings log-rank analysis and Kaplan-Meier method were used. RESULTS: Seventy four CABG patients (36%) had SDNN <93ms while 132 patients (64%) had normal overall HRV (SDNN>/=93ms). The average time of follow-up period was 3.0+/-1.8years. In the follow up period 16 (7.8%) adverse coronary events were recorded. Out of the 16 CABG patients, 13 patients had decreased HRV and 3 had normal HRV (p=0.001). CONCLUSIONS: Contrary to previous reports, results of this study show that the CABG patients with postoperative decreased HRV have a higher mortality rate than patients with normal HRV.