Implantable cardiac defibrillators (ICDs) have evolved prominently since their introduction, with broader indications as primary prevention. ICDs have become complex and offer many programmable parameters. A physician should be thoroughly familiar with the nuances of each model to confirm or dispute the diagnosis made by the ICD as well as to reprogram the parameters with a view to adapting them specifically to the characteristics of individual device recipients. A systematic stepwise approach (clinical history, physical examination, radiographic techniques, and an analysis of the stored electrograms) is essential for correctly identifying the cause of suspected defibrillator malfunction.