Objectives : This study was designed to investigate heart rate variability(HRV) in patients with abnormality on EKG by power spectrum analysis of HRV. Methods : The patient group consisted of 147 patients diagnosed as abnormal on EKG at the Oriental Medical Hospital of Dong-eui University from November 2003 to September 2005. We divided the patient group into 9 subgroups (bradycardia, arrhythmia, PVC, AF, AV block, RBBB, LVH, cardiac ischemia, LAD ). The control group consisted of 117 patients who were diagnosed as normal on EKG at the same hospital during the same period. We checked HRV of the two groups over 5 minutes and compared the HRV index between groups. Results and Conclusions : In the time domain analysis, SDNN was significantly higher in the PVC and AF groups than control group and RMSSD was significantly higher in the all patient group and the bradycardia, PVC and AF groups than in the control group. In the frequency domain analysis, Ln(LF) was significantly higher in the all patient group and the PVC and AF groups than the control group but lower in the LAD group. Ln(HF) was significantly higher in The all patient group and bradycardia, PVE and AF groups than control group. LF/HF ratio was significantly lower in the all patient group and bradycardia, arrhythmia, AF, AV block and LAD groups than control group. The autonomic nerve system and parasympathetic nerve system were higher in the patient group with abnormal EKG compared with the control group.