In a recent communication1it was pointed out that periods of unconsciousness in patients with auriculoventricular dissociation are associated with transient seizures of ventricular fibrillation much more commonly than has been suspected hitherto. Attention was called to the fact that a clinical diagnosis of transient ventricular fibrillation may be suspected in such patients if preceding a period of unconsciousness the heart rate has been noted to increase above that of the usual basic rate. Within the past few months we have been able to confirm these findings in another woman with complete auriculoventricular dissociation and transient syncopal seizures in whom some of the premonitory periods preceding the attacks of unconsciousness resembled those observed in our previous case. However, on careful study of the electrocardiograms obtained at the same time that the patient was observed clinically, another type of cardiac mechanism was found to precede the periods of unconsciousness. In