Patients suffering from heart failure disease have to regularly measure and document health data such as weight and blood pressure. Currently, the data gets lost or is not recorded on a regular basis due to missing reminders and lack of motivation in patients. To address these problems, we introduce a concept for an electronic heart diary (EHD), a mobile application that supports in data collection and motivates the patient. The requirements towards a digital heart diary were collected in discussions with stakeholders in a collaborating hospital. The EHD, allows patients to record their measurement data or even transfer it from a health device to the app. The data is stored in a database that can be accessed with permission of a patient by health professionals through a web application for monitoring purposes. In this way, a worsening of the disease can be detected in an early stage and actions can be taken. This can increase patient safety and prevent rehospitalisation. For motivation and supporting a long-term use of the app, we included methods for gamification and nudging into the application.