REsynchronization Comparison In LBBB and Normal or Mildly Reduced VENTricular Function With CRT (REINVENT-CRT)

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