Blood pressure and heart rate were monitored in narcoleptic dogs by means of a chronically implanted catheter placed in the descending aorta. Changes in these variables were recorded during spontaneously occurring cataplectic episodes. We found no reliable change in blood pressure associated with cataplexy onset. However, heart rate showed a marked increase prior to the onset of cataplexy, with peak heart rates being reached at or shortly after the disappearance of muscle tone. Autonomic events correlated with increased heart rate may contribute to the triggering of cataplexy in narcoleptics.