Inclusion Criteria:

I. DAVID I patients enrolled in the VVI-40 who are hemodynamically stable.

II. Patients with an LVEF 0.40 considered for ICD therapy because of one of the following primary, spontaneously occurring, sustained events within the last 6 weeks prior to enrollment:

• VF arrest (ACC/AHA indication Class 1-1),
• VT with syncope (ACC/AHA indication Class 1-1 or 1-2),
• Non-syncopal sustained VT with significant cardiac symptoms or BP < 80 (ACC/AHA indication Class 1-2, IIb-4),

OR

III. Patients considered for ICD therapy because of one of the following:

• LVEF < 0.40 with inducible VT or VF within 6 weeks prior to randomization (with or without spontaneous arrhythmia), or
• LVEF < 0.30 with coronary artery disease, > 1 month from a myocardial infarction, and > 3 months from bypass surgery or percutaneous coronary intervention.

If the ICD was already implanted at time of consideration for enrollment, the device must have been programmed in the VVI mode since implant.

Exclusion Criteria:

• NYHA CHF Class III unless on optimal heart failure therapy for at least 3 months prior to enrollment,
• NYHA CHF Class IV,
• Reversible causes of the VT/VF event,
• Permanent pacemaker,
• First degree AV block with PR interval of more than 240 ms.,
• 2nd or 3rd or advanced degree heart block,
• Symptomatic bradycardia,
• Pre-existing endocardial pacing leads,
• Permanent atrial fibrillation (>= 6 months or unknown duration),
• Patient awaiting a cardiac transplant,
• Life expectancy <1 year,
• Frequent uncontrolled atrial tachyarrhythmia, or
• Inability to obtain informed consent.