To further improve individual health and well-being, access to high quality and safe services, eHealth interoperability is a fundamental prerequisite. A mature interoperability between health systems will support health services organization and delivery, and improve citizens' awareness of how to prevent disease and preserve good health. Within this context, health institutions have to solve interoperability problems or prevent them to appear, and if possible avoid them before they occur by adapting good practices toward interoperability. This paper proposes an evaluation of the potential health interoperability using the MMEI methodology (Maturity Model for Enterprise Interoperability). It discusses how the MMEI model can be used to help institutions to avoid interoperability problems. A use case for a particular hospital is more closely examined.