Alternating hemiplegia is a rare condition presenting with episodes of hemiplegia, epileptic seizures and, at times, dysautonomic attacks. De novo ATP1A3 (Na(+)/K(+) ATPase subunit) mutations were recently found to be the most common cause. We report a patient with alternating hemiplegia with de novo ATP1A3 mutation who experienced new-onset episodes of collapse in early adulthood unrelated to seizures. An implantable cardiac loop recorder documented episodes of asystole up to 5 s long. Subsequently a permanent pacemaker was implanted. ATP1A3 heart expression may be the explanation for the association of alternating hemiplegia and asystole episodes. Alternating hemiplegia has been associated with an increased risk of sudden death and lethal cardiac arrhythmias may be causative. Patients may need referral for appropriate cardiac investigations, especially if there is a change in symptoms. This case highlights the importance of clinical vigilance in patients with alternating hemiplegia.