Background: Cardiovascular disease is a leading cause of death globally causing 31% of all deaths worldwide. The Danish health care system is characterized by fragmented delivery of services and rehabilitation activities. The Teledialog Telerehabilitation Program for cardiac patients was developed and tested to rectify fragmentation and improve the quality of care. The Teledialog program was based on the assumption that a common communication platform shared by health care professionals, patients, and relatives could reduce or eliminate the fragmentation in the rehabilitation process and improve cooperation between the health professionals. Objective: This study aimed to assess the interorganizational cooperation between health care professionals across sectors (hospitals, municipal health care centers) in a cardiac telerehabilitation program. Methods: Theories of networks between organizations, the sociology of professions, and the "community of practice" approach were used in a case study of a cardiac telerehabilitation program. A triangulation of data collection techniques were used including documents, participant observation (n=76 hours), and qualitative interviews with healthcare professionals (n=37). Data were analyzed using NVivo 11.0. Results: The case study of cooperation in an interorganizational context of cardiac telerehabilitation program is characterized by the following key themes and patterns: (1) integrated workflows via a shared digital rehabilitation plan that help integrate workflow between health care professions and organizations, (2) joint clinical practice showed as a community of practice in telerehabilitation developed across professions and organizations, and (3) unifying the organizations as cooperation has advanced via a joint telerehabilitation program across municipalities and hospitals. Conclusions: The Teledialog Telerehabilitation Program was a new innovative cardiac program tested on a large scale across hospitals, health care centers, and municipalities. Assessments showed that the Teledialog program and its associated technologies helped improve interorganizational cooperation and reduce fragmentation. The program helped integrate the organizations and led to the creation of a community of practice. Further research is needed to explore long-term effects of implementation of telerehabilitation technologies and programs.