Abstract: A ventilation air pressure oscillation mitigation device for a ventilator includes a housing defining an inlet and an outlet. The device includes a valve seat defining a primary opening and a plurality of secondary openings. A valve body is selectively positionable in a first position and a second position within the device. In the first position, substantially all of a first flow of ventilation air from the inlet to the outlet passes through the primary opening. When the valve body is in the second position, all of a second flow of ventilation air from the inlet to the outlet passes through the plurality of secondary openings. An actuator controls a position of the valve body.