The periaqueductal gray matter (PAG) is an essential neural substrate for central integration of defense behavior and accompanied autonomic responses. The dorsal half of the PAG (dPAG) is also involved in mediating emotional responses of anxiety and fear, psychological states which often are associated with changes in ventilation. However, information regarding respiratory modulation elicited from this structure is limited. The present study was undertaken to investigate the relationship between stimulus frequency and magnitude on ventilatory pattern and respiratory muscle activity in urethane-anesthetized, spontaneously breathing rats. Electrical stimulation in the dPAG recruited abdominal muscle activity, increased ventilation, and increased respiratory frequency by significantly shortening both inspiratory time (Ti) and expiratory time (Te). Ventilation increased within the first breath after the onset of stimulation and the respiratory response increased with increasing stimulus frequency and magnitude. dPAG stimulation also increased baseline EMG activity in the diaphragm and recruited baseline external abdominal oblique EMG activity, normally quiescent during eupneic breathing. Significant changes in cardiorespiratory function were only evoked by stimulus intensities greater than 10 µA and stimulus frequency was greater than 10 Hz. Respiratory activity of both the diaphragm and abdominal muscles remained elevated for a minimum of 60 seconds following the cessation of stimulation. These results demonstrate that there is a short latency respiratory response elicited from the dPAG stimulation which includes both inspiratory and expiratory muscles. The changes in respiratory timing suggest rapid onset and sustained post-stimulus dPAG modulation of the brainstem respiratory network that includes expiratory muscle recruitment.