To demonstrate a reduction in the number of ventricular therapies (ATP and Shocks) delivered for treating spontaneous arrhythmia episodes with a fast cycle length (CL≤ 320ms) as a consequence of self-termination and better arrhythmia discrimination due to a greater number of R-R intervals necessary to detect ventricular events.

Primary Objective:

The primary objective is to demonstrate a 20% reduction of ventricular therapies (ATP and Shocks) delivered for treating spontaneous arrhythmia episodes with a fast cycle length (CL ≤ 320 ms) by choosing a number of 30 out of 40 intervals to detect (NID) compared to a NID of 18 out of 24 in subjects with either Class I or IIA indication for ICD implantation, regardless of cardiac resynchronization capabilities.

Secondary Objectives:

1. Evaluate the percent reduction in the number of shocks delivered per subject for treating spontaneous episodes with a fast cycle length (CL ≤ 320 ms) and for spontaneous ventricular episodes.
2. Evaluate the efficacy of ATP in successfully treating spontaneous ventricular episodes (CL: 200ms-320ms) for subjects in primary and secondary prevention in both arms of the study.
3. Evaluate acceleration rate or degeneration into VF of spontaneous episodes (CL of 200ms-320ms) due to ATP therapy in the two study arms.
4. Compare the likelihood of syncopal events associated with spontaneous episodes with a fast cycle length (CL ≤ 320 ms).
5. Describe the economic impact and the quality of life consequences.

Inclusion Criteria:

• Either ICD or CRT+ICD indications (Class I-IIA) according to the current AHA / ACC / ESC guidelines.
• Previous implant of a Medtronic device including "ATP During Charging" feature for 15 days at the maximum.

Exclusion Criteria:

• ICD replacements and upgrading.
• Brugada Syndrome, Long QT and HCM patients
• Ventricular tachyarrhythmia associated with reversible cause.
• Other electrical implantable devices (Neurostimulators, etc.).
• Subject's life expectancy less than 1 year.
• Subject on heart transplant list which is expected in less than 1 year.
• Subject is <18 years of age, or the subject is under a minimum age that is required as defined by local law
• Women who are pregnant or women of childbearing potential who are not on a reliable form of birth control.
• Unwillingness or inability to provide written informed consent.
• Enrolment in, or intention to participate in, another clinical trial.
• Inaccessibility to come to the study center for the follow-up visits.
• Mechanical tricuspid valve.