This study examines the interoperability issues of Health care Information Systems, (HIS). With the evolution of big data, Internet of Things, smart devices, Value Based Health care and categorization of patient groups for outcome measurements there is a great need for better HISs which in an effective way is able to share data with each other. Standardization is one recognized way of achieving interoperability in information systems. Hence, in this case study we have researched the architectural drivers of hospital which incorporates interoperability and which interoperability characteristics can be standardized via existing health carefocused open standard. Our results, gathered via nine semi-structured interviews and analyzed through a thematic analysis, show that HISs objectives are hindered by both design constraints and by technical, semantic and process interoperability issues. It also shows that there are open standards which are applicable to these, however this raised the question of why they in a broad scale are not. We therefore also discuss the possibility of adding a forth category to the three previous forces that in make up interoperability [15], [26]. This forth force we call interoperability climate and it is defined as: Organizations’ readiness to interact with each other under unanimously defined terms. It is inspired by the ”climate of innovation” and ”innovation value-fit” in the theory of Innovation Implementation by Klein & Sorra [16]. It incorporates the idea of how a bad climate of innovation and low intensity innovation value-fit can prevent interoperability in HISs.