In-body Energy harvesters are becoming increasingly interesting for the development of battery-less implantable devices. This paper presents novel ultra-low fully integrated power management interface powered by heart’s mechanical motions with power optimization and impedance matching between the transducer and the functional load. The paper proposes integrated power interface that can potentially help in resolving the power limitation issues and provide options for optimizing tradeoffs between ultra-low power and other performance matrices in deep-tissue implantation for medical devices. The proposed power management interface circuit has been designed in 0.18-um CMOS technology, and the simulated power consumption of 189.8 nW while providing two voltage outputs of 1.4 V and 4.2 V. The simulation results show an output power 8.2x times of an ideal full-bridge rectifier without an external power supply. The design proposes the potential of self-powered operational heart implantable devices as it is capable of cold startup to provide stable output voltages.