Implantable cardioverter defibrillators (ICDs) terminate ventricular tachycardia (VT) and ventricular fibrillation (VF) with high efficacy. ICDs improve mortality in patients after survived sudden cardiac death (SCD) and in patients at high risk of dying suddenly. All trials which show a benefit of ICD therapy, have performed some kind of defibrillation testing in order to prove correct system function, sensing of VF and effective defibrillation. Current devices show a shock efficacy of 80–90 % for singular shocks and devices provide up to seven rescue shocks. The probability that a device does not terminate an episode of VT or VF should therefore be very low. However, it is difficult to abandon defibrillation testing because prospective data is lacking that demonstrate non-inferiority, if ICDs are implanted without some kind of test. Two prospective trials are on the way and will be finish by 2013/14: the SIMPLE and NORDIC trial, which will answer the question if defibrillation testing can be abandoned without any effect on the benefit of ICD therapy or if testing may even be harmful.