The proposal for a European Health Data Space (EHDS) aims to improve secondary utilization of health data. However, it remains challenging to balance interests of different stakeholders to identify an appropriate governance system. The multitude of claims have often been negotiated under the umbrella term of data ownership. We adopt the four conceptual poles of data ownership proposed by Hummel, and conduct 28 expert interviews to identify the practical relevance of these poles. All poles are mentioned, albeit with varying frequency. There is a broad consensus regarding the potential of utilizing health data in the collective interest. Actors from the data economy prioritize the potential of data as a marketable resource. Intermediaries and researchers emphasize the importance of providing individuals with control mechanisms. The study closes a gap by transferring abstract conceptualizations of data ownership into practice and highlighting implications for the further development of the EHDS.