Background: St Jude Medical “Riata” implantable cardioverter-defibrillator leads have a higher-than-expected failure rate and carry a Class 1 recall. Failure usually relates to an insulation breach that may not be identified by lead fluoroscopic or electrical changes. Case presentation: We report a case of Riata lead failure identified by the aborted delivery of effective therapy for ventricular fibrillation at the time of defibrillation threshold testing. Lead fluoroscopic appearances were normal. Shock impedance on attempted shock delivery was unrecordably low, and all other electrical parameters were within normal limits. Conclusion: Riata lead failure may be unrecognised until there is failure to deliver necessary therapy. Strong consideration ought to be given to lead examination under high-voltage shock delivery through the device.