Resynchronization for Ambulatory Heart Failure Trial in Patients With Preserved LV Function

Inclusion Criteria: * Patients with NYHA class II-IVa HF symptoms and are on diuretic therapy * LVEF \> 35% (stratify by LVEF 36-49% and LVEF ≥ 50%), and recovered LVEF (previously LVEF ≤ 35%, but improved to LVEF \> 35% with medical therapy) * Patients with LVEF ≥ 50% must also have either left atrial enlargement (any of the following: LA diameter ≥3.8 cm, LA length ≥5.0 cm, LA volume ≥55 ml, LA volume index (LAVi) ≥29 mL/m2) or LV hypertrophy (LV mass index (LVMI) ≥115 g/m2 for males and ≥ 95g/m2 for females) * LBBB and QRS duration ≥ 140 msec. for men or ≥ 130 msec. for women, and with mid-QRS notching or slurring in ≥ 2 leads * Patients may have permanent RV pacing with a QRS duration ≥180ms * Patients may have permanent atrial fibrillation with good rate control defined as a resting heart rate of ≤80 bpm at rest and ≤110 bpm with 6-minute walk test * NT-proBNP ≥ 600 pg/ml on stable medical therapy without previous heart failure hospitalization in the last 12 months, or ≥400 pg/ml on stable medical therapy if there was a heart failure hospitalization within the previous 12 months * Appropriate pharmacological treatment of HF and co-morbidities. * Stable diuretic and other HF medications for at least four weeks Exclusion Criteria: * Serum creatinine \>180 μmol/L; or estimated glomerular filtration rate \[eGFR\] ≤30 mL/min/1.73 m2, calculated using the Modification of Diet in Renal Disease formula * In-hospital patients with acute cardiac or non-cardiac illness that requires intensive care * Acute coronary syndrome (including MI) \<4 weeks * Coronary revascularization (CABG or PCI) \< 3 months * Uncorrected or uncorrectable primary valvular disease * TAVI \< 3 months * Restrictive, or reversible form of cardiomyopathy, cardiac amyloidosis * Severe primary pulmonary disease such as cor pulmonale, primary pulmonary hypertension (may include secondary pulmonary hypertension, if mean pulmonary pressure is ≤ 70 mm Hg) * Expected to undergo cardiac transplantation within one year (status I) * Patients with a life expectancy of less than one year from non-cardiac cause. * Patients included in other clinical trials that will affect the objectives of this study * Patients who are pregnant/intend to get pregnant * Those unable or unwilling to provide informed consent