Ventilator circuit aerosol delivery systems used to administer medication to a patient are disclosed. In one implementation, a metered dose inhaler (“MDI”) ventilator assembly may include a housing that defines an interior space, an inhalation port that defines an inhalation passageway in communication with the interior space, an exhalation port that defines an exhalation passageway in communication with the interior space, a patient port that defines a patient passageway in communication with the interior space, and a MDI receptacle positioned on the housing and in communication with the interior space. The MDI receptacle is operative to receive a MDI container and dispense an aerosolized medication within the MID container into the interior space so that during inhalation, an inhalation flow including the aerosolized medication may flow through the inhalation port, the interior space, and the patient port. Conversely, during exhalation, gases, moisture, condensation, and/or mucus expelled from the patient flow through the patient port, the interior space, and the exhalation port.