Abstract: A device for introducing a rotatable atherectomy catheter into an artery of a patient comprises an elongated hollow introducer sheath attached to the distal end of a housing formed with a bore in which is mounted a seal. The seal is formed with an expandable opening to selectively prevent fluid flow through the seal. The seal includes a plurality of penetrable disks serially mounted in the bore. A permutation of slits and holes in the disks provides an assembled relationship allowing penetration of the seal by a catheter, while also preventing fluid leakage from the seal. The device includes a seal expander and a rear connector. The seal expander is engageable with the housing attached to the sheath, and the connector is engageable with the expander. The expander provides an insertion tube for penetrating the seal which expands to form a fluid tight seal around the insertion tube. The connector provides a second seal for preventing fluid leakage from the connector during operation of the rotatable catheter.