The primary objective is to evaluate the S-ICD system's ability to identify and terminate induced ventricular fibrillation in patients during the implant procedure. The safety and performance of the S-ICD system will also be assessed throughout the patient follow-up period.

Inclusion Criteria:

• Replacement of an existing implanted transvenous ICD system
• Class I, Class IIa, or Class IIb ACC/AHA/HRS indications for patients without an existing transvenous ICD system
• Age is >= 18 years
• Appropriate pre-operative ECG as measured with a specially developed template

Exclusion Criteria:

• Subjects unable or unwilling to provide informed consent
• Any condition which precludes the subject's ability to comply with the study requirements
• 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 the S-ICD system trial without written consent from the sponsor.
• 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 with impaired kidney function as measured by a Cockcroft-Gault Glomerular Filtration Rate (GFR) with a GFR <= 29.