An interventional medical system comprising an implantable medical device and a catheter for delivering the device to an implant site, the catheter comprising an elongate shaft including a proximal portion, a distal-most portion, and a handle, the proximal portion being secured to the handle and including a sidewall that defines first and second lumens extending alongside one another and along a length of the proximal portion, the distal-most portion including an internal shoulder and a sidewall defining a receptacle, the receptacle having a distal opening defined by a distal terminal end of the distal-most portion sidewall, and the receptacle being sized to contain the implantable medical device therein with a proximal end of the device abutting the internal shoulder, and the distal opening being sized to allow passage of the device therethrough; the catheter further comprising a sheath and a deflection assembly including the handle, a control member subassembly and an elongate pull wire, the pull wire extending from a proximal end thereof to a distal end thereof and within the first lumen of the proximal portion of the shaft, the distal end of the pull wire being secured to the distal-most portion of the shaft and the control member subassembly being mounted to the handle and coupled to the proximal end of the pull wire, the control member subassembly being configured to move the pull wire along the length of the proximal portion of the shaft; characterised by the catheter comprising: a coiled spring member including one or more proximal turns secured to the proximal portion of the shaft, one or more distal turns secured to the distal-most portion of the shaft, and a plurality of open-pitch turns therebetween, the spring member defining a transition lumen that extends along a longitudinal axis of the spring member, the transition lumen being in fluid communication with the first and second lumens of the proximal portion of the shaft and the receptacle of the distal-most portion of the shaft, the open-pitch turns being arranged to be pre-loaded by a longitudinal compression thereof, the one or more proximal turns of the spring member having a first diameter, and the one or more distal turns of the spring member having a second diameter, the second diameter being greater than the first diameter; and further characterised by the sheath overlaying the coiled spring member and being configured to allow a bending of the spring member; the pull wire extending alongside the coiled spring member and the control member subassembly being configured to control the bending of the coiled spring member via the pull wire by moving the pull wire along the length of the proximal portion of the shaft. a coiled spring member including one or more proximal turns secured to the proximal portion of the shaft, one or more distal turns secured to the distal-most portion of the shaft, and a plurality of open-pitch turns therebetween, the spring member defining a transition lumen that extends along a longitudinal axis of the spring member, the transition lumen being in fluid communication with the first and second lumens of the proximal portion of the shaft and the receptacle of the distal-most portion of the shaft, the open-pitch turns being arranged to be pre-loaded by a longitudinal compression thereof, the one or more proximal turns of the spring member having a first diameter, and the one or more distal turns of the spring member having a second diameter, the second diameter being greater than the first diameter; and further characterised by the sheath overlaying the coiled spring member and being configured to allow a bending of the spring member; the pull wire extending alongside the coiled spring member and the control member subassembly being configured to control the bending of the coiled spring member via the pull wire by moving the pull wire along the length of the proximal portion of the shaft.