Abstract  Implantable cardioverter-defibrillators (ICDs) have a proven mortality benefit in appropriately selected people. Several retrospective studies, though, have postulated that appropriate ICD therapy may lead to fatal, pulseless electrical alternans (PEA). This case report describes an episode of transient PEA from myocardial stunning and standstill following defibrillation threshold testing. The risk of post-shock myocardial stunning and standstill should be kept in mind as a potential complication of testing. With rapid recognition and prompt intervention, this complication is potentially reversible.