This study presents a non-genetic, semiconductor-enabled biomodulation platform for high spatiotemporal photostimulation of cardiac systems. The platform uses monolithic silicon-based photoelectrochemical devices to achieve precise and tunable optical pacing of cardiac tissues. The devices were characterized for their spatiotemporal profiling of photoelectrochemical currents, demonstrating high precision, accuracy, and resolution. In vitro, the devices successfully paced cultured cardiomyocytes (CMs) and isolated rat hearts, and in vivo, they were effective in pacing rat and mouse hearts, even in the presence of ischaemia. The platform also demonstrated reliable multisite pacing in a pig heart model, achieving biventricular pacing and closed-thoracic optical stimulation. The study highlights the potential of this leadless, lightweight, and multisite photostimulation platform for cardiac resynchronization therapy (CRT), offering a promising alternative to traditional electrical pacing systems.This study presents a non-genetic, semiconductor-enabled biomodulation platform for high spatiotemporal photostimulation of cardiac systems. The platform uses monolithic silicon-based photoelectrochemical devices to achieve precise and tunable optical pacing of cardiac tissues. The devices were characterized for their spatiotemporal profiling of photoelectrochemical currents, demonstrating high precision, accuracy, and resolution. In vitro, the devices successfully paced cultured cardiomyocytes (CMs) and isolated rat hearts, and in vivo, they were effective in pacing rat and mouse hearts, even in the presence of ischaemia. The platform also demonstrated reliable multisite pacing in a pig heart model, achieving biventricular pacing and closed-thoracic optical stimulation. The study highlights the potential of this leadless, lightweight, and multisite photostimulation platform for cardiac resynchronization therapy (CRT), offering a promising alternative to traditional electrical pacing systems.