A standard pacemaker can improve a patient's quality of life and may even prolong it, but conventional pacemakers contain leads and batteries, which have their own complications. Hence, the need for a pacemaker with leadless and batteryless capabilities is becoming increasingly important, as it reduces infection risk, device failure, and patient discomfort. Unlike other leadless pacing technologies, the proposed method in this work does not require a battery or leads. More specifically, a novel leadless pacemaker was proposed that harvest energy from radio frequency (RF), using a metamaterial-based rectenna, to power the pacemaker and stimulate the myocardium. Initially, path loss in the body was computed by performing experiments on ovine models and available RF power, deep inside the body, was estimated. These baseline specifications were then used to design an implantable rectenna, which was simulated and optimized using Advanced Design System (ADS) and ANYS-High Frequency Structure Simulator (HFSS). The performance of the antenna was initially tested in vitro and was then integrated with a separately designed rectifier circuit using a matching circuit. The resulting module, when integrated with a pacing circuit, formed a leadless and batteryless pacemaker and was then implanted at the left ventricle of an ovine model. This prototype demonstrated that leadless pacing, using a RF-based energy harvesting method, can be achieved. Furthermore, to improve the overall form factor and achieve a conformal design, a numerical model for the deeply implantable antennas, in HFSS, was characterized. Finally, this proposed model was validated analytically as well as experimentally, and was also used to design a conformal implantable antenna for the leadless pacing application. This research has strengthened the possibility of leadless pacing using the RF energy harvesting method and has paved the way for future research in this area. Indeed, this proposed technology has the potential to bring transformational possibilities, not only to leadless pacing, but also to other deeply implantable biomedical devices.