Abstract: An iris-type valve assembly for controlling a flow of fluid. The assembly comprises a base member, a rotatable member, and an elongated elastomeric valve sheath. The distal end of the valve sheath is secured to the base member and the proximal end of the valve sheath is secured to the rotatable member. At least one of the valve sheath ends includes a flange that is secured to a valve-receiving surface of the base member or the rotatable member. The base member and the rotatable member are aligned to define an elongated passageway therethrough for passage of an interventional device, and the elastomeric valve sheath is disposed along the passageway and has a longitudinal opening therethrough for passage of the interventional device. Upon rotation of the rotatable member relative to the base member the longitudinal opening of the valve sheath is selectively constrictable to comprise a seal around the interventional device.