A metered dose aerosol actuator, for use in association with a pressurized medicament container provided with a dispensing metering valve having a valve stem, including a housing adapted to receive the container, a stem block extending upwards from the base of the housing and adapted to engage the valve stem by means of a cavity provided in the stem block, the stem block being provided with a spray orifice adapted to be in flow connection with the valve stem and the cavity, a sump extending downwards from the cavity relative to the spray orifice, wherein the sump has a smooth, rounded interior surface.