Background: Real-time spectral mapping using fast Fourier transformation (FFT) during sinus rhythm (SR) has been used for identifying the substrate with structural inhomogeneity in which the intracardiac electrogram (IEGM) has unusually high frequency (HF). Non-inducibility of targeted arrhythmias is one of troublesome situations encountered during electrophysiologic study (EPS). Methods: Eight patients including 5 patients with ventricular tachycardia (VT) from right ventricular outflow tract (RVOT) (51짹8, female=4), and 3 control patients (60짹7, female=1) who needed EPS for other reasons. The electro-anatomical mapping (EnSite 3000���) was conducted and obtained IEGM at multiple sites within RV, focused on OT, during SR in each patient. These IEGMs were put into the real-time spectral analysis using FFT and constructed 3D geometry. The site with dominant frequency (DF) was targeted as the substrate of RVOT VT, and we ablated without VT induction or pace mapping. Results: IEGMs obtained in 118짹62 RV sites. The DF zones in 3D DF maps were observed in septal and/or anteroseptal region of RVOT in all VT patients, but not in the control. Mean DF of these regions were 60.9짹11.9 Hz. The DF was higher than other sites in RVOT (39.6짹5.3, P=0.038). The DF of same region of RVOT in control patients was 35.1짹3.3 Hz, which was not different from that of surrounding areas 27.9짹4.3 Hz. Acute procedural success was achieved in all five patients. During 5짹1 month of follow-up, couplets of premature ventricular complex were observed in one patient. Conclusion: Real time spectral mapping using FFT might localize the arrhythmogenic loci (so-called ���PVC nest���), and be useful for the ablative treatment in patients with non-inducible RVOT VT.