Ischemic ventricular tachycardia (VT) causes more than half of the 300,000 sudden cardiac deaths (SCD) that occur annually in the United States. Implantable cardioverter defibrillators (ICDs) are the standard of care, but they are expensive (the total cost of an ICD implant exceeds $80,000) and not curative. Patients who receive ICDs are subject to periodic shocks to halt episodes of VT, and those shocks can be traumatic. RF ablation represents a potential method for curing VT, and at a much lower cost than ICDs, but while RF ablation has been successful at treating atrial arrhythmias, it has not so far been as effective at treating VT. An ablation tool capable of treating VT has the potential to eliminate the need for ICD implants, greatly reducing the cost to the health care system of treating VT while also improving the lives of patients affected by VT. We have developed an ablation system and catheter for the treatment of VT. Our technology delivers heated saline along with RF energy, and is unique in its ability to treat the large volumes of cardiac tissue necessary to eliminate arrhythmogenic tissue located deep in the ventricular wall. Our technology is capable of treating much larger volumes of tissue than conventional RF because saline carries the heat generated by RF into tissue by convection. We have demonstrated that our ablation system can cure VT in an infarcted animal model. Our primary aim is to carry out a 20-patient clinical trial to establish the safety of our technology and to begin to demonstrate the efficacy of the Thermedical system for treatment of VT. Before beginning the human clinical trial, we will complete verification and validation activities to ensure the electrical safety of the system and the biocompatibility of the catheter materials, and to validate the catheter packaging and sterilization. Additionally, prior to the human trial we will carry out a final safety study on 8 infarcted canines. We will conduct the 20-patient study at the Mayo Clinic. Patients will be eligible for the study if they have recurrent, symptomatic VT; if they have failed prior cardiac catheter VT ablation; if the etiology of the arrhythmia is related to ischemic structural heart disease; and if a target arrhythmia has been treated by an implanted ICD. The primary safety endpoints of this study will be the absence of Major Adverse Cardiac Events (MACE) prior to hospital discharge in more than 70% of the patients, and the absence of serious adverse events that are potentially device related within 30 days for more than 70% of the patients. The primary efficacy endpoints of the study will be non-inducibility of the clinical VT and treatment of clinically relevant scar.