The article describes the process of the development of an app to support people in lifelong secondary prevention, e.g. after a heart attack or with chronic diseases. The goal of this app-guide, called the HealthNavigator, is to coach people walking on leisure paths through guidance, motivation, and better understanding of physical abilities (body awareness). There were three development cycles, each one followed by a demonstrator test with health professionals and patients. The outcomes of these tests were taken into account for the following development cycle. Focus was placed on how to motivate people to exercise regularly and in a healthy manner. The evaluations showed that HealthNavigator was found to be usable tool for teaching body awareness and making users feel safe, while motivating them to take walks in the open air.