A number of studies have shown that the implantable cardioverter-defibrillator (ICD) is the most effective therapy for the prevention of sudden cardiac death from ventricular arrhythmias in patients with ischemic heart disease and severe left ventricular dysfunction. However, ejection fraction should not be considered the only parameter for the identification of candidates to ICD; this may lead to a "hyper-simplification" of the choices and to often unnecessary or inappropriate implantations. The purpose of this paper was to review the literature data regarding indications for ICD implantation in primary prevention in patients with severe ischemic left ventricular dysfunction by taking into account different clinical settings, in particular the biological age, the comorbidity profile, the temporal length between the ischemic event and ICD implantation, the possible impact of revascularization in reducing the arrhythmic risk.