Primary Objective - To determine if implantation of a permanent CRT pacing device (with LB-CRT, or conventional BiV-CRT with a coronary sinus LV lead) can improve electromechanical function, HF symptoms, and natriuretic peptide levels among patients with symptomatic HF, LVEF > 35%, and LBBB.

This pilot study will be a multicenter randomized controlled trial involving 20 medically stable outpatients with heart failure (HF), preserved or mildly reduced LVEF (>35%), and LBBB. Patients will undergo implantation of a Medtronic Percepta CRT-P with an atrial lead, left bundle branch area pacing (LBBap) lead, and a LV lead. They will then be randomly allocated in a 1:1 fashion to usual care plus LB-CRT (DDD 60-130, LV lead turned off) (active intervention #1) or usual care plus BIV-CRT (DDD 60- 130, LV lead turned on) (active intervention #2).

Inclusion Criteria:

• Ability to understand and the willingness to sign a written informed consent form and HIPAA Authorization.
• Stated willingness to comply with all study procedures and availability for the duration of the study
• Male or female aged ≥18 years
• Strict LBBB defined as QRS duration ≥130ms in women and ≥140ms in men, a QS or rS complex in V1 and V2, as well as notching or QRS slurring in mid-QRS in ≥2 contiguous leads.
• NYHA II/III, ambulatory NYHA IV, or NYHA I HF with any prior history of HF symptom decompensation requiring hospitalization, ED visit, or outpatient visit for care with IV diuretic
• LVEF >35% by clinically obtained echocardiogram overread by the study core-lab
• Demonstration of adequate echocardiographic images to allow for assessment of endpoints
• On a stable guideline directed HF medical regimen
• For females of reproductive potential: use of a highly effective contraception for at least 1 month prior to screening and agreement to use such a method during study participation
• Ability to understand and the willingness to sign a written informed consent form and HIPAA Authorization.

Exclusion Criteria:

• Patients with anticipated addition or titration of HF medical therapies (ACE/ARB/ARNI, beta blocker, MRA, SGLT2 inhibitor) during the duration of the study
• Treatment with another investigational drug or other intervention within 3 months
• Current unrevascularized coronary artery disease, unstable angina, acute MI, CABG, or PCI within the past 3 months
• Significant non-functional mitral or aortic valvular disease (severe stenosis or regurgitation)
• Significant structural heart [including hypertrophic cardiomyopathy (septal thickness ≥15 mm) or infiltrative cardiomyopathy (eg. amyloid)]
• Current moderate to severe pulmonary hypertension (right ventricular systolic pressure of ≥40 mmHg)
• Oxygen dependent chronic lung disease
• Prolonged episodes of AF (>3 days or an AF burden >10%) within the preceding 3 months
• Presence of cardiac pacemaker or implantable cardioverter defibrillator
• Prior mechanical tricuspid valve replacement
• Pregnancy or lactation due to concerns about the effect of radiation from the pacemaker implantation procedure on the fetus
• Known allergic reactions to components of the pacemaker or leads
• Febrile illness within 3 days of trial enrollment
• Parents/guardians or participants who, in the opinion of the Investigator, may be non-compliant with study schedules or procedures.
• Control Participant Exclusion Criteria: same