Medical information systems are in perpetual evolution which makes them different from each other in each hospital. These different systems compose a heterogeneous, distributed system with high complexity. Thus interoperability of medical information systems is one of the main challenges of the IT society. Semantic interoperability in healthcare is especially important when all the varying types of data need to interact.A lot of works tried to solve even partially this problem of interoperability. This paper highlights the most relevant of them and presents a comparative study between new technologies and research trends to resolve heterogeneity issues of medical information systems.