Aspects of an expandable sheath can be used in conjunction with a catheter assembly to introduce a prosthetic device, such as a heart valve, into a patient. Such aspects can minimize trauma to the vessel by allowing for temporary expansion of a portion of the introducer sheath to accommodate the delivery apparatus, followed by a return to the original diameter once the prosthetic device passes through. Some aspects can include a sheath with a variable diameter inner liner wound in a spiral slidable configuration and an outer layer. The disclosed sheath is configured to expand from a predetermined rest diameter dr to an expanded diameter de during application of a radial outward force by passage of a medical device through the sheath.