eHealth Lifestyle Intervention To Enhance Outcomes in HFpEF

The goal of this clinical trial is to learn if a digital lifestyle education program improves exercise capacity in adults who have heart failure with preserved ejection fraction (HFpEF) and overweight or obesity. HFpEF is a type of heart failure in which the heart muscle is stiff and does not relax well, even though its pumping strength looks normal. The main questions it aims to answer are: * Does the program improve how much oxygen participants can use during exercise, a measure of fitness, after 6 months? * Does the program improve participants' quality of life and help them lose weight? Researchers will compare a group that uses the digital program plus usual care to a group that receives usual care alone. This will show whether the program adds a benefit. Participants will: * Be placed by chance into one of the two groups * Use a study website with short videos on exercise, healthy eating, and managing stress (program group), with new content every week for 6 months * Have exercise tests, an ultrasound scan of the heart, blood tests, and complete a quality-of-life questionnaire at the start and after 6 months Both groups will keep taking their usual heart failure medicines.

Inclusion Criteria: * Age over 18 years * Body mass index (BMI) over 27 kg/m² * Symptoms consistent with heart failure * Left ventricular ejection fraction (LVEF) of 50% or higher * Elevated NT-proBNP according to the European Society of Cardiology age-adjusted rule-in thresholds: 125 pg/mL or higher if under 50 years, 250 pg/mL or higher if 50 to 75 years, and 500 pg/mL or higher if 75 years or older * Echocardiographic abnormalities: left ventricular hypertrophy, left atrial enlargement, or diastolic dysfunction Exclusion Criteria: * Body mass index (BMI) over 40 kg/m² * Life expectancy of less than 1 year * Chronic kidney disease on renal replacement therapy * Moderate or greater valvular heart disease * Inability to exercise