Abstract: An apparatus for controlling fluid flow within a host body has a first shell and a second shell for coupling with the second shell to form a cylindrical object suitable for engaging and surrounding a selected canal with the host body. The cylindrical object is open at both ends and has an interior diameter of a dimension making it suitable for fitting over the selected host body's canal, such as the urethra. The apparatus also includes a plunger for constricting the fluid flow when activated. The plunger may be activated by an electrical solenoid or hydraulic or pneumatic activation to move from a free-flow position into a constricting position wherein the fluid flow though the canal is substantially prevented or reduced. The apparatus can be used for controlling incontinence or restricting fluid flow in other body canals.