Background; Radiofrequency catheter ablation (RFCA) of hemodynamically unstable ventricular tachycardia (VT) was investigated in 7 patients with structural heart disease; 3 with prior myocardial infarction (ICMP), 4 with idiopathic dilated cardiomyopathy (DCMP). Methods; Seven subjects who had monomorphic VTs refractory to drug therapy including amiodarone IV were enrolled. Two of them had frequent shocks by implantable cardioverter-defibrillator (ICD) and 2 had electrical storm. VT was induced by programmed ventricular stimulation and mapped using non-contact mapping system (ESI 3000) for 5 - 10 seconds, and then cardioverted or defibrillated by DC. Off-line analysis of wave-front dynamics during VT was performed to identify the earliest activation (EA) and/or the exit point, critical isthmus, and scar zone by substrate mapping. Results; Six males and one female were included in this study: mean age 55.9 짹 18.1 years (range 23 - 78 years). Mean left ventricular ejection fraction was 35.4 짹 11.2 %. 21 different monomorphic VTs (mean cycle length 312 짹 59 ms, range 220 - 445 ms) in 7 patients were induced. The EA point was identified in - 59 짹 43 ms before QRS onset and the exit point was identified in - 7 짹 12 ms before QRS onset. RF was delivered at the EA (n=18), exit (n=19), isthmus (n=13), and surrounding area of scar zone (n=3). 18/21 VT (85.7%) in 5/7 patients (71.4%) were successfully ablated. In 2 patients with remnant VT, clinically documented VTs were abolished by RF application into the narrow isthmus of the reentrant circuits of VT. At a follow-up of 18.4 짹 14.1 months, all of ICMP and 2 of DCMP were free from VTs. Recurrent documented VT was identified in one of 6 patients with initially successful RFCA, but this episode was well controlled by anti-arrhythmic agents. No major complication occurred. Conclusions; Given the favorable acute and clinical long-term results, RFCA using non-contact mapping system can be effectively applied to abolish and control hemodaynamically unstable VT. This approach appears to be more effective in patients with ischemic cardiomyopathy.