Patient involvement has often been defined and examined on the basis of conceptual theoretical frameworks. This article explores patient involvement contextually and locally, in encounters between patients and healthcare professionals in cardiac rehabilitation in Denmark. With inspiration from institutional ethnography, the goal is to unpack what involvement actually implies in rehabilitation activities. The analysis provides micro-sociological insights into how patient involvement is constituted and institutionally conditioned and shows how textually mediated ruling relations regulate activities and interactions, shaping patient involvement in local practices. The analysis reveals how patient involvement primarily relates to healthcare professionals involving patients in health knowledge. It explores how national guidelines and local instructions for healthcare professionals frame understandings of patient needs and problems. The concluding discussion highlights how patients have limited opportunities to influence their own care process. It also points out how it is left to the individual healthcare professional to solve contradictions between institutionally defined tasks and the ambition of patient involvement.