Health information features significant spatial-temporal and domain complexities, which brings challenges to the implementation of patient-centered, interoperable and semantically coherent healthcare information systems. This position paper supports the idea that the multilevel modeling approach is essential to ensure interoperability at the semantic level, but true interoperability is only achieved by the adoption of open standards, and open source implementations are needed for promote competition based on software quality. The Multilevel Healthcare Information Modelling (MLHIM) specifications are presented as the fully open source multilevel modeling reference implementation, and best practices for the development of multilevel-based open source healthcare applications are suggested.