The main objective of this study is to compare the time from randomization to the first recurrence of any ventricular tachycardia (VT) in patients undergoing VT ablation (for stable VTs) and substrate ablation (for unstable VTs) after an initial episode of stable VT and patients not undergoing ablation, with both groups under the protection of an ICD.

The main objective of this study is to compare the time from randomization to the first recurrence of any VT in patients undergoing VT ablation (for stable VTs) and substrate ablation (for unstable VTs) after an initial episode of stable VT and patients not undergoing ablation, with both groups under the protection of an ICD.

Prior to the ablation, the patients will undergo electrophysiologic study (EPS) with programmed ventricular stimulation, with the aim to reproduce the clinical VT. Most patients with coronary artery disease, systolic LV dysfunction, and one episode of clinical sustained VT have more than one inducible VT at electrophysiologic study. Since any inducible VT can become a potential clinical VT (24), an attempt will be made to ablate the clinical stable VT, as well as all inducible morphologies, stable or unstable.

One of the following 2 ablation strategies will be possible for each VT:

• Substrate modification in sinus rhythm in case of unstable induced monomorphic VT which does not allow mapping and ablation in tachycardia, or noninducible stable clinical VT.
• VT ablation in tachycardia in case of stable VT

For each procedure the number of tachycardias , the type of each tachycardia (inducible or noninducible, stable or unstable), the ablation strategy for each tachycardia (it is possible that lesions deployed for one tachycardia will render another tachycardia noninducible as well) and the procedural outcome for each tachycardia will be documented.

Inclusion Criteria:

• Coronary artery disease For the purpose of this study, coronary artery disease will be defined as the presence of a 50 % or more diameter stenosis of the left main coronary artery, or 75 % or more diameter stenosis of the left anterior descending, circumflex or right coronary arteries, or the history of a surgical or percutaneous revascularization procedure, or history of successful thrombolysis, or a history of prior myocardial infarction (e.g.: documented by Q-wave, R-reduction, aneurysm)
• Left ventricular ejection fraction ≤ 50 % as estimated by echocardiography or contrast ventriculography within the previous 30 days and evidence for old myocardial infarction (ECG, echocardiographic or venticulographic).
• One episode of documented stable clinical VT without any reversible causes
• Written informed consent

Exclusion Criteria:

• Age < 18 years or > 80 year
• Protruding LV thrombus on pre-ablation echocardiogram
• Acute myocardial infarction within the preceding 1 months
• Class IV NYHA heart failure
• Valvular heart disease or mechanical heart valve precluding access to the left ventricle
• Unstable angina
• Cardiac surgery involving cardiotomy (not CABG) within the past 2 months
• Serum creatinine > 220 mmol/L (2.5 mg/dL)
• Thrombocytopenia or coagulopathy
• Contraindication to heparin
• Pregnancy
• Acute illness or active systemic infection
• Other disease process likely to limit survival to less than 12 months
• Significant medical problem that in the opinion of the principal investigator would preclude enrollment in the study
• Participation in another investigational study
• Unwillingness to participate or lack of availability for follow-up
• Incessant VT or electrical storm
• Bundle branch reentry tachycardia as the presenting VT
• Preexisting ICD