Abstract: Apparatus and method for delivering over-sized or large bore devices through passageways in the body. The apparatus comprises an elongated inflatable balloon havinq an inner diameter slightly larger than the outer diameter of the device to be introduced into the passageway. A guidewire may be utilized to assist introduction of the balloon into the bodily passageway. A device introduction chamber is attached at the proximal end of the balloon for temporarily housing the device being introduced into the passageway, and the device itself includes a delivery shaft at least partially disposed in the introduction chamber. An inflation device is provided for inflating the balloon with a biologically compatible fluid once the balloon has been inserted into the bodily passageway. The distal portion of the balloon is inserted into the bodily passageway, the balloon is then inflated to expand and straighten the passageway, and the device may then be advanced through the balloon into the passageway.