We observed, during Holter recording, a case of inferior acute myocardial infarction complicated by paroxystic hyperkinetic atrial fibrillation, which occurred 12 min after the onset of acute irreversible myocardial ischemia. The atrial fibrillation was preceded by a complex pattern of hyperkinetic supraventricular arrhythmias characterized by single premature supraventricular beats, paired premature supraventricular beats and many runs of paroxystic supraventricular tachycardia. The most plausible hypothesis is that atrial fibrillation and the preceding arrhythmic pattern have been due to an extension of ischemia from ventricular to atrial myocardium.