During this double-blind randomized cross-over study, patient will receive during 18 months treatment 1 (hydroquinidine or placebo) and, after 7 days of wash-out, patient will receive treatment 2 (meaning for example hydroquinidine if treatment 1 was placebo). Time length before arisen of an appropriate shock registered on the defibrillator (meaning due to ventricular arrhythmia) will be assessed during treatment 1 period and treatment 2 period.We hypothesized that hydroquinidine administration will enhance time length before arisen of an appropriate shock and thus mean that hydroquinidine administration can prevent heart from appearance of ventricular arrhythmia. Patient's defibrillator recordings will be analysed every 6 months plus when patient experiences an ICD shock. If the shock delivered by the ICD is appropriate and happens during treatment 1 period, patient will switch to treatment 2 period after 7 days of wash-out. If the shock delivered by the ICD is appropriate and happens during treatment 2 period, study will be finished for this patient.Before starting the study, each patient will test which dose of hydroquinidine she/he requires to have an hydroquinidine concentration in her/his blood included between 3 and 6 µmol/L.