The INSURE trial is a multi-center, prospective trial to collect information about adequate ICD therapies in ICD patients before & after their first elective ICD replacement. For this purpose all consecutive ICD patients will be included in the study, whose first implanted device is replaced due to ICD battery depletion (i.e. arrival at battery indicator ERI). ICD replacements due to other reasons can be included if duration of first ICD implantation was > 3 years. All patients included in the trial are regularly followed up until delivery of their first adequate ICD therapy. The collected data shall provide statistically valid information about the risk to patients who never have experienced adequate ICD therapy before the ICD replacement investigated in this study. In the future, these statistical risk data can give additional information to implanting physicians, such as whether an ICD replacement can eventually be omitted in those patients who are at very low risk for the occurrence of ICD therapies. All actually available GUIDANT ICDs with CE certificate can be implanted in this trial.