Abstract Background Regular physical activity is paramount in heart failure (HF) patients and, due to its well-established benefit in quality of life, functional capacity and prognosis, carries a Class I indication in international guidelines. However, satisfactory compliance rates remain suboptimal, which is largely attributable to unavailability or suboptimal utilization of comprehensive cardiac rehabilitation programs. Digital health application-based telerehabilitation, on the other hand, has emerged as a potentially valuable tools in enhancing risk factor control and lifestyle modification rates in this high-risk patient population. Purpose In this study, we aimed to investigate whether the use of a purpose-designed Internet of Things (IoT)-based e-health system could lead to a clinically relevant increase in physical activity in a cohort of patients with HF across the spectrum of left ventricular ejection fraction (LVEF). Methods Nineteen HF patients were enrolled in the study. Subjects' key clinical characteristics are summarized in Picture 1. All subjects were provided with: a) a set of medical devices with wireless connectivity, b) a state-of-the-art smartwatch and c) a latest-generation smartphone, to which a dedicated patient application was installed. The latter was coupled with a web-based platform designed for physician use, forming the patient-physician interface (PFI). On top of standard-of-care verbal and written exercise recommendations, study physicians also prescribed individualized, guideline-directed exercise regimens for each patient via the PFI, which, in turn, delivered to subjects notifications upon detection of deviations (Picture 2). The first month of participation -during which the smartwatch was used as an activity tracker but exercise notifications had not been activated- served as the baseline period; baseline physical activity level in steps per day was then compared to the respective value measured during each of the 5 following months. Results Mean baseline-to-peak increase in daily step count was calculated at 23.34% (-20.33 - 103.63%). A baseline-to-peak increase in physical activity level of at least 20% was observed in 9/19 patients, with 6 more demonstrating a baseline-to-peak increase in the order of magnitude of 15-19.99%. Only 3 patients failed to achieve any increase in daily step count average. However, after the study month in which the peak physical activity value was observed (typically in the 2nd-4th study month), mean daily step count declined to baseline again in all but 2 patients. Conclusions Despite the study's non-randomized design and small sample size, our results suggest that mobile application-based telerehabilitation constitutes a promising approach in HF patients’ care, as it could aid them achieve a clinically relevant increase in physical activity; this effect, however, can be transient, and this highlights the importance of continued physician oversight.Picture 1: Clinical characteristicsPicture 2: Exercise prescription example