Cardiovascular diseases belong to the most common causes of death. Telehealth applications can help to improve therapy and support behavior change. It was the objective of the present work to construct and evaluate within a trial (25 patients) an automated feedback system for a telehealth application to support behavior change. We used a rule-based approach and constructed 26 rules in 9 categories. Rule design and implementation followed the principles of the Austrian Medical Product Law, resulting in an automated rule-based feedback system. Evaluations show high user satisfaction with 80% of all users perceiving the system as useful.