This study evaluates the impact of a new pacing mode avoiding unnecessary ventricular stimulation in combination with advanced dual chamber detection with slow VT management on the clinical outcome for hospitalization and mortality and inadequate therapy in medically stable, ICD-indicated patients with impaired left ventricular function (LVEF ≤ 40%) who do not have pacing indications and no indication for Cardiac Resynchronization Therapy (CRT). It compares a new pacing mode avoiding ventricular stimulation when not needed combined with dual chamber detection with a pure ventricular back up pacing and single chamber detection criteria with pure ventricular back up pacing. Therapies are compared in a prospective, randomized, single-blinded, parallel trial with a 24-month randomized treatment period. Randomization follows a 1:1 ratio. ICD therapy is enabled for all patients throughout the study. All patients receive optimal drug therapy for arrhythmia and heart failure treatment.