UW-Madison researchers have developed an integrated, self-charging leadless intracardiac pacemaker (LIP) that is solely powered by a double-oscillatory triboelectric nanogenerator (TENG) that is capable of generating a volumetric power density of 276 μW cc-1 driven by heartbeats. This high output is enabled by a multi-fold triboelectric architecture with precisely engineered geometry and elasticity, as well as a device design that uses the pacemaker’s packaged electronic components as the inertial mass to drive oscillation of the triboelectric nanogenerators, minimizing the overall size and weight of the device. The triboelectric architecture also allows consistent energy output regardless of heart motion direction or body posture. The miniaturized TENG can fit within the battery compartment of a commercial Medtronic Micra™ LIP, allowing standard femoral-venous delivery by commercial catheters. When implanted in the heart of a swine model, the device delivers stable, rate-responsive electrical energy in vivo, which reliably supports the cardiac pacing function for heart rates control at physiological levels. Long term intracardiac implantation confirmed secure fixation, unaffected cardiac function, and minimal tissue reaction of the fully integrated device.