BACKGROUND AND RATIONALE: In patients with ischemic or non-ischemic cardiomyopathy and impaired left ventricular ejection fraction, treatment with implantable cardioverter-defibrillator (ICD) has been shown to improve survival and guidelines recommend their use for primary prevention of sudden cardiac death. Experts disagree regarding the validity of decade-old trial results as the basis for this recommendation, therefore, reconsideration of prophylactic ICD treatment is needed. EU-CERT-ICD, DANISH-ICD AND DO-IT: In order to update the evidence on prophylactic ICD treatment, several prospective studies are underway in Europe. The prospective EU-CERT-ICD cohort study (NCT 02064192) is enrolling 2500 patients and compares patients undergoing first ICD implantation with controls with an earlier clinical decision to go without ICD implantation strictly unrelated to the study. The DANISH ICD study (NCT 00542945) has randomized 1000 patients with dilated cardiomyopathy and an LVEF ≤35% (1:1 ICD implantation vs. control). The prospective DO-IT multicenter registry will include 1500 ICD patients in multiple Dutch high-volume implanting centers. Due to the widespread use of ICD therapy, new randomized trials seem not straightforward to envisage in many countries. CONCLUSION: The above described ICD studies will provide additional evidence regarding the effectiveness of primary prophylactic ICDs in Europe and may have an impact on ICD treatment guidelines. They could also help to design randomized trials in low risk patients.