PROJECT SUMMARY/ABSTRACT Heart failure with preserved ejection fraction (HFpEF), a syndrome characterized by exercise intolerance due to breathlessness and fatigue, is a major public health problem rising in prevalence. No pharmacologic strategy has been shown to improve exertional symptoms in HFpEF patients, but exercise training is beneficial. For this reason, guidelines strongly recommend that patients with HFpEF engage in regular exercise. Despite this recommendation, physical activity in patients with HFpEF is dismally low, and a recent NHLBI working group identified strategies to increase adoption and adherence to physical activity recommendations among patients with HFpEF as a research priority. Insights from behavioral economics have been shown to both better reflect the ‘predictable irrationality’ of humans and to be effective in designing interventions that achieve sustained improvements in health behavior. Our group has tested the ability of interventions guided by behavioral economic insights using our NIH-funded Way to Health software platform, which captures physical activity from wearable devices and automates the processing of incentives and feedback. In randomized controlled trials enrolling obese patients and older adults with or at risk for atherosclerotic vascular disease, we have shown that interventions using gamification and social incentives increase physical activity during 3-month interventions, which are sustained over 3-month follow-up. If these effects could be translated to patients with HFpEF, it would represent a safe and readily implementable exercise strategy that could lead to sustained improvements in quality of life and functional capacity, and heart failure hospitalizations in a cohort of patients with few therapeutic options. In this study, we propose to conduct a 3-arm randomized, controlled trial with a 6-month intervention and then a 3-month follow-up period to address the following aims: Aim 1: To evaluate the effectiveness of gamification plus either ‘support’ or ‘competition’ to increase adherence to physical activity in HFpEF patients. Aim 2: To evaluate whether increased adherence to physical activity recommendations in the intervention arms translates to improved quality of life and functional capacity. Aim 3: To determine the association between increases in step count and improvements in quality of life and functional capacity, establishing a minimum clinically important difference in daily steps for patients with HFpEF. If this low-cost, highly scalable intervention increases adherence to physical activity recommendations and improves quality of life, it would warrant a larger trial to assess its effects on HF hospitalizations.