FitHeart is a behavior change intervention to promote long-term adherence to a healthy lifestyle for patients with heart disease. There are many components of cardiac rehabilitation; the main focus of the mobile app will be on physical activity tracking and motivation. The app will be used in the context of existing clinical care, so there shall also be additional features that do not need to be the focus of the mobile apps core functionality, but shall be addressed with a simple education page or set of links. Please review the SDD and RSD for additional details.