A system for introducing a delivery apparatus into a patient's vasculature. The system may include a sheath having a lumen and configured to be inserted into the patient's vasculature. An introducer has a channel for receiving a guide wire and is configured to be positioned within the lumen of the sheath. A plug is coupled to the introducer and is configured to move from a first position in which the plug has a first diameter to a second position in which the plug has a second diameter that is greater than the first diameter and greater than the interior diameter of the sheath, the plug being configured to slide within the lumen in a direction from the distal end of the sheath towards the proximal end of the sheath to expand the sheath in the direction radially outward from the lumen.
