Sophisticated diagnostic information is provided by the latest generation of implantable defibrillators. The success of therapy and the type of therapy successful in terminating ventricular arrhythmias is provided by interrogating the ICD device. In addition, R to R interval information can be retrieved. In selected devices, either local bipolar electrograms from the rate sensing leads or wide bipolar electrograms from the energy delivering leads provide visual confirmation of the presence of ventricular tachyarrthythmic events leading to therapy. The value and limitations of this sophisticated diagnostic information in providing insight into the electrical events triggering therapy and the events triggering ventricular arrhythmias are discussed.