The implantable cardioverter-defibrillator (ICD) therapy is an established intervention for the prevention of sudden cardiac death (SCD) in patients with significant left ventricular dysfunction. Multiple randomized clinical trials have studied the use of ICD for the primary and secondary SCD. These studies were performed in patients with left ventricular dysfunction from coronary artery disease or dilated cardiomyopathy, and the marker of reduced ejection fraction has emerged for selecting patients who would benefit from ICD therapy. Currently, for most of these patients the decision to implant, or not, is determined by relatively straightforward paradigms. The same cannot be said for the genetic cardiac diseases associated with SCD - long QT syndrome, Brugada syndrome, hypertrophic cardiomyopathy, and arrhythmogenic right ventricular dysplasia. Indications for ICD in these conditions are very much a work-in-progress.