Home monitoring of cardiac patients with an implantable cardioverter-defibrillator (ICD) holds promising benefits such as improved mortality rates, but HCI research shows that patients dislike the passive role imposed by current home monitoring technology. In this paper, we report from a study on how cardiac patients reacted to taking on a more active role of being a diagnostic agent. We developed and implemented a technology probe for reporting symptoms and other health metrics to health providers daily and studied ten ICD patients interacting with the probe for eight weeks. Our analysis resulted in three themes; patient reflection and obsession, patient roles and responsibility towards healthcare staff, and opportunities for nurses to use reports at the hospital. We contribute to HCI research on home monitoring by discussing the role of the diagnostic agent and the potential for implanted chronic patients to engage in collaborative interpretation with health providers.