Background: The use of mobile health applications (apps) is an effective strategy in supporting patients' self-management of heart failure (HF) in home settings, but it remains unclear whether they can be used to reduce sedentary behaviors and increase overall physical activity levels. Aim: The aims of this study were to determine the effect of an 8-week home-based mobile health app intervention on physical activity levels and to assess its effects on symptom burden and health-related quality of life. Method: In this study, we collected repeated-measures data from 132 participants with HF (60.8 ± 10. 47 years) randomized into a usual care group (n = 67) or an 8-week home-based mobile health app intervention group (n = 65). The intervention was tailored to decrease the time spent in sedentary behavior and to increase the time spent in physical activities performed at light or greater intensity levels. Physical activity levels were monitored for 2 weeks before the intervention and during the 8-week intervention using the Samsung mobile health app. Heart failure symptom burden and health-related quality of life were assessed at baseline, 2 weeks from baseline assessment, and immediately post intervention. Results: At week 8, all participants in the intervention group demonstrated an increase in the average daily step counts above the preintervention counts (range of increase: 2351-7925 steps/d). Only 29 participants (45%) achieved an average daily step count of 10000 or higher by week 6 and maintained their achievement to week 8 of the intervention. Repeated-measures analysis of variance showed a significant group-by-time interaction, indicating that the intervention group had a greater improvement in physical activity levels, symptom burden, and health-related quality of life than the usual care group. Conclusion: Home-based mobile health app-based interventions can increase physical activity levels and can play an important role in promoting better HF outcomes.