Support is requested for a Keystone Symposia meeting entitled Cell Biology of the Heart: Beyond the Myocyte- Centric View, organized by Peter Kohl, Robert G. Gourdie and Stefanie Dimmeler. The meeting will be held in Copper Mountain, Colorado from March 1-6, 2015. The general topic of this meeting is relevant to the NHLBI mission with respect to the broad area of cardiac structure and function research. The heart is a muscle, and as such, much of the basic and applied research into cardiac structure and function has focused on cardiac myocytes. However, the majority of heart cells are non-myocytes. Prominent examples include cells comprising the coronary vasculature, fat, connective tissue (e.g., fibroblasts), nerves, and immune cells. It has become increasingly clear that these cells are not merely bystanders of myocyte function, but active participants with important signaling roles that contribute to cardiac development, cell differentiation, and functio of the healthy and diseased heart. This Keystone Symposia meeting will be unique in that, for the first time, it will bring together the internationally-leading experts in the field of non-myocte contributions to cardiac structure and function. It aims to address: 1) Roles of non-myocytes for cardiac cell fate determination and development; 2) Mechanisms of non-myocyte - myocyte signaling interactions; 3) Effects of these interactions in normal and diseased heart; and 4) Relevance of non-myocytes as targets for therapeutic interventions. The symposium benefits from being scheduled in parallel to a symposium dedicated to myocyte development and regeneration. The obvious synergies of the two topics are highlighted by joint sessions and keynote lectures at the start and the end of the meeting, serving as a conceptual frame from origin to post-injury involvement of the different cardiac cell types. As a result, participants wil leave this meeting with a more holistic understanding of the heart as a multi-cellular organ, and a broadened horizon to support their individual research. This will be the first high-level symposium with an explicit focus on reviewing the current state of a new frontier of cardiac cell biology: non-myocyte roles in the development, regulation, and adaptation of the cardiac performance. The symposium will contribute to a paradigm shift that is taking place in the field, driven by the appreciation that a myocyte-centric view of the heart will always be limited in its ability to deliver the mechanistic understanding of cardiac structure and function that is required for improved predictive and therapeutic action. Aided by the parallel symposium design, this event will bring together investigators from a broad range of backgrounds and conceptual approaches, who normally publish in different journals and attend separate meetings.