A system for delivering an implantable medical device includes a loading assembly and a catheter. The loading assembly includes a deployment member and a sidewall defining a chamber into which the device may be pulled through a distal opening thereof, so that the sidewall holds fingers of the device's fixation member in an extended condition while a temperature in the chamber is lowered. When the chamber is connected to the catheter, advancing the deployment member pushes the device, with fixation fingers in the extended condition, into a delivery lumen of the catheter. With the catheter positioned within a patient, the device can be pushed into a distal portion of the catheter while a relatively cold fluid is infused through the delivery lumen. While holding the deployment member in place, retracting the catheter exposes the device fixation fingers out from the lumen, for engagement with tissue at the implant site.