Hybrid electric vehicles require careful dealing with EMC because in HEV's analog and digital circuitry coexist in the vehicle's enclosed environment. These lead to a requirement of advanced methods for the increased requirements for electromagnetic compatibility and analysis and reduction of EMI . There are many methods to increase EMI resistance of a hybrid car's electronics systems implemented printed circuit board, several of which will be reviewed in the current paper. In this review paper, we explain conducted and radiated emission avoidance methods using isolation amongst several subsystems. Within the harsh EM environment of a modern hybrid car, isolation between systems of differing frequencies is an effective method for reducing EMI/EMC issues. These techniques include usage of filters to hinder conducted emissions and shielding to stop radiated emissions. Of the many parameters which need to be tweaked to improve the electromagnetic compatibility of a system, the use of filters at the boundaries of shielded systems (to increase resistance to RF and transient susceptibility issues). In hybrid electric vehicles, electronic power converters produce EM noise with high-powered low frequency harmonics and high-frequency low powered electronic noise is produced from in-vehicle communication systems. More research is required in the field where there is a requirement to separate devices operating at high and low frequency spectrum ranges at the same time. We attempt to show several solutions to these class of EMI problems present in mixed frequency environments through the use of separation of systems.