Pacing in Heart Failure With Preserved LVEF

Inclusion Criteria: 1. Clinical features consistent with heart failure. All patients will have symptoms of moderate to severe heart failure with New York Heart Association (NHYA) classification III or IV symptoms (for at least 3 months). 2. LV Ejection Fraction less or equal to 50%, with no evidence of significant valvular disease, no hypertrophic or restrictive cardiomyopathy, and no evidence of pericardial constriction. 3. Additionally all patients will have demonstrated evidence of septal flattening during exercise using contrast echocardiography. 4. Adults (over 18 years) 5. Negative test for Covid during surgical pre-assessment, and adherence to prescribed self-isolation before implantation. 6. Two weeks or more following final dose of vaccination against coronavirus. Exclusion Criteria: 1. Inability to provide informed consent. 2. Enrolment in other clinical studies. 3. BMI more than 35 4. Objective evidence of significant lung disease on formal lung function testing 5. Previous (within three months) or scheduled coronary revascularisation or other cardiac surgery 6. Acute coronary syndrome (within the previous three months) 7. History of atrial fibrillation (AF) 8. Renal insufficiency requiring haemodialysis 9. Life expectancy less than 6 months 10. Prosthetic heart valves 11. Blood coagulation disorders 12. Immunocompromised patients (e.g. AIDS, patients on steroids, cytotoxic drugs, and radiation therapy) 13. Currently pregnant, or intending to conceive. 14. Recent positive Covid test (up to 14 days prior to pre-assessment).