Devices, systems, and methods deliver implantable medical devices for ventricular-from-atrial (VfA) cardiac therapy. A VfA device may be implanted in the right atrium (RA) with an electrode extending from the right atrium into the left ventricular myocardium. A flexible leed, or another probe, may be advanced to the potential implantation site and used to identify a precise location for implantation of a medical device, such as an electrode, leadlet, lead, or intracardiac device. Some methods may include locating a potential implantation site in the triangle of Koch region in the right atrium of a patient's heart; attaching a fixation sheath to the right-atrial endocardium in the potential implantation site; and implanting the medical device over a guide wire at the potential implantation site. An implantable medical device may include an intracardiac housing and a leadlet, which may be delivered by these methods.