Inappropriate discharge is still a major issue of implantable cardioverter defibrillator therapy. The diagnostic options of modern devices facilitate classification of the underlying abnormality.A 65-year-old woman with depressed left ventricular performance received spurious shocks from an ICD, implanted for ventricular tachycardia. A lead fragment of an explanted VVI pacemaker system could be identified as cause of erroneous ventricular fibrillation detection by the ICD. The electrical noise caused by interaction between the lead remnant and the ICD lead was detectable even on the surface ECG.Based on our findings, removal of fragmented lead material should be considered prior to ICD implantation, to avoid potentially adverse and harmful interactions with ICD systems.