Embodiments of the present disclosure are directed to cannulating devices and methods for exchanging cannulating devices in an endoscopic procedure. In one implementation, an apparatus for endoscopic operations is described. The apparatus includes a cannulating device to be introduced through an internal lumen of an endoscope via a biopsy port. The cannulating device has an elongated body. The elongated body includes a guidewire lumen configured to receive a guidewire therein, and a slit extending over at least a portion of the length of the elongated body from a distal tip to a proximal position of the elongated body.