The purpose of this study is to determine if patients implanted with a St. Jude Medical (SJM) implantable cardioverter defibrillator (ICD) will benefit by using AutoIntrinsic Conduction Search (AICS) rather than only a programmed AV/PV delay. This study will compare the two methods of programming with respect to intrinsic activity.

Inclusion Criteria:

• Patient has been implanted with a dual chamber SJM ICD with AICS for 1 month (± 2 weeks).
• At the time of enrollment, patient is paced in the right ventricle (RV) ≤25% of the time as determined by the device diagnostics.
• Patient is medically stable.

Exclusion Criteria:

• Patient has evidence of atrioventricular (AV) block (first, second or third degree) such that ventricular pacing would be required as part of the patient's routine management
• Patient is unable to comply with the follow-up visits due to geographical, psychological, or any other reasons.
• Patient is younger than 18 years of age.
• Patient is pregnant.