Introducer sheath with expandable introducer

A system for introducing a delivery apparatus into a patient's vasculature, the system comprising:

• a sheath having a distal end, a proximal end, an interior diameter, a lumen, and a length extending from the distal end to the proximal end, the sheath being configured to be inserted into the patient's vasculature and to expand in a direction radially outward from the lumen;
• an introducer having a channel for receiving a guide wire and being configured to be positioned within the lumen of the sheath;
• and
• a plug coupled to the introducer and 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 in the first position being configured to fit within the lumen, and the plug in the second position having a length that is less than the length of the sheath and 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.