Cardiovascular disease is a growing problem recently. There has been a few attention in the study of ventricular repolarization duration variability. RDV is associated with some cardiac diseases. We studied vagal blockade effects on RDV in urethane-anesthetized rats. To study the relation between ventricular repolarization duration and autonomic nervous system in subjects, we changed the balance of autonomic nervous system by body posture. The HRV and RDV spectral analysis showed that HF peak was modulated by the frequency of controlled respiration. We also found a significant decrease in HFnu and increase in LF/HF in HRV and RDV during vagal blockade. There is a significant increase of LF/HF of subjects in HRV and RDV from supine to tilt, which is consistent with the state of autonomic nervous system. The result of our study is that the ventricular repolarization duration is dependent on the autonomic nervous system. The RDV analysis will be more helpful in the clinic. This approach will provide a more useful noninvasive evaluation of cardiac disease and function.