The role of arterial baroreceptors in maintaining mean arterial blood pressure was evaluated when intermittent positive pressure ventilation with and without positive end-expiratory pressure (PEEP) was used to ventilate dogs. The decrease in mean arterial pressure (MAP) during mechanical ventilation is a result of decreased cardiac output which is a result of a restriction to venous return. Dogs had monitoring devices applied so hemodynamic variables could be measured under 4 ventilatory conditions: spontaneous, intermittent positive pressure (IPPV), IPPV with PEEP (5 & 10 cmH2O), and recovery (spontaneous) in both an open-loop (carotid sinus feedback removed) and closed-loop (feedback intact) condition. Responses were also compared before and after bilateral cervical vagotomy which eliminates afferent input from cardiopulmonary receptors. When the animals were neurally intact, the initiation of IPPV resulted in no change in MAP due to a significant increase in heart rate. With the application of PEEP, there was a significant decrease in MAP which was buffered by significant increases in heart rate and vasomotor tone as compared to denervated animals. Either carotid sinus or cardiopulmonary baroreceptors were capable of regulating and maintaining an adequate MAP but were not capable of restoring cardiac output and oxygen delivery. The effects on the cardiovascular system during the use of IPPV and PEEP dictates close monitoring of patients for decreased cardiac output.