Our results of HRV analyzed by frequency spectrum are similar to Tatiana Mironova (2017), she studied HRV on 123 CABG patients and found that HRV indices all decreased LF (17.84 ± 10.83 with 15.23 ± 6.11), HF (25.76 ± 12.53 with 15.7 ± 4.78) were significant when comparing preop and postop (p<0.05).