An expandable introducer assembly for use in inserting a medical device into a body vessel of a patient, said expandable introducer assembly comprising: a dilator extending along an axis from a proximal dilator end to a distal dilator end; an expandable sheath extending from adjacent said distal dilator end in surrounding and coaxial relationship with said dilator for concurrent insertion and axial advancement with said dilator into the body vessel of the patient; an introducer subassembly including a hemostasis valve releasably interconnected to said proximal dilator end and an introducer sheath extending in surrounding and coaxial relationship with said dilator from said hemostasis valve to next adjacent said expandable sheath; said expandable sheath including a sheath hub interchangeable from a locked condition for preventing axial movement of said dilator and said introducer subassembly relative to said expandable sheath during the insertion of said expandable introducer assembly into the body vessel and an unlocked condition for allowing concurrent axial advancement of said introducer subassembly and said dilator relative to said expandable sheath after the insertion of said expandable introducer assembly into the body vessel to allow said introducer sheath to pass through said sheath hub and into said expandable sheath for radially expanding the body vessel; and characterized in that it further comprises a coupler releasably connected to said sheath hub and disposed in interlocked relationship with said hemostasis valve when said hemostasis valve is axially advanced towards said sheath hub for allowing serial retraction of said introducer sheath and said expandable sheath out of the body vessel of the patient, wherein said coupler includes a receiving body for establishing said releasable connection to said sheath hub and said interlocked relationship with said hemostasis valve, and said coupler including a tether (122, 222, 322, 422, 522, 622) extending between said receiving body and said sheath hub and expandable from a collapsed condition to a taught condition during axial retraction of said introducer subassembly for facilitating said serial retraction of said introducer sheath and said expandable sheath out of the body vessel of the patient. a dilator extending along an axis from a proximal dilator end to a distal dilator end; an expandable sheath extending from adjacent said distal dilator end in surrounding and coaxial relationship with said dilator for concurrent insertion and axial advancement with said dilator into the body vessel of the patient; an introducer subassembly including a hemostasis valve releasably interconnected to said proximal dilator end and an introducer sheath extending in surrounding and coaxial relationship with said dilator from said hemostasis valve to next adjacent said expandable sheath; said expandable sheath including a sheath hub interchangeable from a locked condition for preventing axial movement of said dilator and said introducer subassembly relative to said expandable sheath during the insertion of said expandable introducer assembly into the body vessel and an unlocked condition for allowing concurrent axial advancement of said introducer subassembly and said dilator relative to said expandable sheath after the insertion of said expandable introducer assembly into the body vessel to allow said introducer sheath to pass through said sheath hub and into said expandable sheath for radially expanding the body vessel; and characterized in that it further comprises a coupler releasably connected to said sheath hub and disposed in interlocked relationship with said hemostasis valve when said hemostasis valve is axially advanced towards said sheath hub for allowing serial retraction of said introducer sheath and said expandable sheath out of the body vessel of the patient, wherein said coupler includes a receiving body for establishing said releasable connection to said sheath hub and said interlocked relationship with said hemostasis valve, and said coupler including a tether (122, 222, 322, 422, 522, 622) extending between said receiving body and said sheath hub and expandable from a collapsed condition to a taught condition during axial retraction of said introducer subassembly for facilitating said serial retraction of said introducer sheath and said expandable sheath out of the body vessel of the patient.