Interventional catheter assemblies that operate over a guide wire are disclosed. Specifically, an elongated flexible catheter is associated at its proximal end with a housing having a guide wire port where the guide wire exits the housing. The housing additionally incorporates a guide wire brake mounted within a slot positioned a distance from the guide wire port for engaging and releasing a guide wire. The slot is generally arranged at an angle to the path of the guide wire as it exits the guide wire port. When the guide wire is clamped in the angled slot, variable lengths of exposed guide wire accumulate in a substantially unrestrained condition when the flexible catheter is advanced and retracted relative to the guide wire, allowing movement of the distal end of the catheter over considerable distances without repositioning and re-clamping the proximal end of the guide wire.
