A catheter 1 suitable for advancement through a body passageway of a patient. The catheter 1 comprises a catheter body 4 which is flexible to provide the necessary trackability for the catheter 1 to advance through a body passageway, and two stainless steel reinforcement wires 5 extending along the catheter body 4 which provide the necessary pushability to advance the catheter 1 through the passageway. The reinforcements 5 are positioned diametrically opposed to one another by approximately 180 degrees on opposite sides of the longitudinal axis of the catheter 1, and the catheter body 4 is relatively soft and twistable. This configuration enables the entire catheter 1 to spontaneously twist during advancement so that the reinforcements 5 orientate themselves along a plane of neutral bending during advancement of the catheter 1. In this way, any resistance to the trackability of the catheter 1 due to the stiff reinforcements 5 is minimised.