A patient with long QT syndrome and a history of palpitations underwent electrophysiologic study. Runs of polymorphic self-terminating atrial tachyarrhythmias were easily induced and occurred spontaneously several times. Atrial monophasic action potential (MAP) durations were prolonged at short pacing cycle lengths. Premature high right atrial extrastimuli prolonged MAP durations in the low right atrium, resulting in an inverse electrical restitution curve, and increased dispersion of repolarization. MAP morphology showed gradually increasing early afterdepolarizations. When the arrhythmia was initiated, a new action potential reproducibly emerged from these afterdepolarizations. To the knowledge of the authors, this is the first reported case of "atrial torsades de pointes" in a patient.