In order to reduce the effort in the integration and actualization of heterogeneous healthcare legacy systems that should share a common database, we propose the creation of an interoperability bus using the HL7 standard—the HL7Middleware. This interoperability bus is an intermediate layer responsible for the communication between a database, health information systems and medical equipment, called HL7Server. Connected systems use the HL7 messaging semantics to store and retrieve data from the database. We validate our approach with respect to two different criteria: performance and integration costs. Benchmark tests were executed with and without the use of HL7Middleware and with different network bandwidths. These results demonstrated that the performance of the interoperability bus is higher when compared to traditional database access for larger volumes of data and when the bandwidth of the user is considerably lower than the bandwidth of the connection between HL7Server and database. The overall development and deployment cost was considered low and the reusability degree of wrapper code was considered high, thus suggesting a progressive reduction of the integration costs of additional services and subsystems of an organization.