Abstract: An apparatus for use in conjunction with a multi-dose inhaler which includes a novel valving mechanism and an expansion chamber which permits medication to be delivered to the patient without the need for precise timing of canister actuation. The apparatus also includes a filter unit for filtering the patient's exhaled breath and also includes a unique baffling arrangement which functions to decrease average aerosol particle size for better targeting the desired lung area. In one form of the invention, the valving mechanism comprises an apertured elastomeric valve member having a top pivot bar which uniquely pivots on a pair of pivot posts provided on proximate the upper margin of a novel valve member engaging, generally planar base.