Although it is well-established that sympathetic activity is modulated with respiration, it is unknown whether neural control of respiration is reciprocally influenced by cardiovascular function. Even though previous studies have suggested the existence of pulse-modulation in respiratory neurons, they could not exclude the possibility that such cells were involved in cardiovascular, rather than respiratory motor control, owing to neuroanatomic and functional overlaps between brainstem neurons involved in respiratory and cardiovascular control. The aim of this study was to test the hypothesis that respiratory motoneurons and putative premotor neurons are modulated by arterial pulse. An existing dataset composed of 72 well-characterized, respiratory-modulated brainstem motoneurons and putative premotor neurons was analyzed using ², a recently described statistic that quantifies the magnitude of arterial pulse-modulated spike activity (12). Neuronal activity was recorded in the rostral and caudal ventral respiratory groups of 19 decerebrate, neuromuscular-blocked, ventilated cats. Axonal projections were identified by rectified and unrectified spike-triggered averages of recurrent laryngeal nerve activity or by antidromic activation from spinal stimulation electrodes. The firing rates of approximately 30% of these neurons were modulated in phase with both the respiratory and cardiac cycles. Further, arterial pulse-modulation occurred preferentially in the expiratory phase in that only expiratory neurons had high ² values and only expiratory activity had significant ² values after partitioning tonic activity into the inspiratory and expiratory phases. The results demonstrate that both respiratory motoneurons and putative premotor neuronal activity can be pulse-modulated. We conclude that a cardiac cycle-related modulation is expressed in respiratory motor activity, complementing the long-recognized respiratory modulation of sympathetic nerve activity.