The purpose is to further evaluate the operation, safety, and feasibility of a subcutaneous implantable defibrillator (S-ICD) system in patients who require an implantable cardioverter defibrillator (ICD)for treating ventricular tachyarrhythmias. The S-ICD electrode and pulse generator emulator will be briefly implanted and tested during the standard implantation procedure of an ICD, but then the S-ICD system will be removed entirely.

The objectives of this study are to further evaluate the S-ICD system's ability to identify and terminate induced ventricular tachyarrhythmias in patients acutely with an S-ICD emulator and parasternal electrode during the implant procedure of a standard transvenous ICD.

The active emulator is not a powered medical device and all elements of the test system are removed following the testing.

This acute intra-operative protocol will test the ability of the electrode and emulator to appropriately convert the arrhythmia and allos an assessment of post shock pacing.

Inclusion Criteria:

• Patients requiring ICD therapy according to National Centre for Clinical Excellence (NICE) criteria are eligible
• And patients who require replacement of an existing transvenous ICD system are eligible

Exclusion Criteria:

• Patients unable or unwilling to provide informed consent
• Any conditions which precludes the subject's ability to comply with the study requirements, including completion of the study
• Females who are pregnant or lactating and pre-menopausal women who are unwilling to use adequate birth control for the duration of the study
• Participation in another investigational device trial at any time during the conduct of this study
• Patients with a serious medical condition and life expectancy of less than one year
• Patients with documented spontaneous and frequently recurring VT that is reliably terminated with anti-tachycardia pacing
• Patients with existing epicardial patches or subcutaneous electrodes in the left thoracic quadrant

patients requiring ICD therapy