Abstract: A medical catheter comprising a distal shaft having a greater flexibility than the proximal shaft. The proximal shaft has a helical end portion of reduced outer diameter which is integral with and extending from the distal end of the proximal shaft. The helical end portion slidingly fits within a portion of the proximal end of the distal shaft. The helical end portion is bonded to at least a portion of the distal shaft to form a fluid-tight seal. The pitch of the helical end portion may be constant or variable. The helical turns may be abutting or spaced apart. A guidewire shaft centrally extends longitudinally through the proximal and distal shaft such that fluid can be transmitted through the proximal and distal shaft, exterior to the guidewire shaft.