This is a prospective, single-arm, non-randomized, non-blinded study designed to characterize the locations of His Bundle (HB) pacing that results in correction of electrical dyssynchrony and to characterize morphology and activation time of local intracardiac electrogram (IEGM) with an electro-anatomical mapping system during a device implant procedure and secondarily to assess the efficacy of HB pacing or HB plus LV pacing (when indicated) in correction of electrical dyssynchrony in heart failure patients with left bundle branch block.

Inclusion Criteria:

1. Patients are undergoing implant of an Abbott pacemaker or CRT device under standard indications
2. An ECG with a wide QRS complex (>130 ms)
3. ECG morphology of typical complete LBBB,
4. Patients have heart failure with NYHA Class II-IV symptoms,
5. LV EF <50%
6. At least 18 years old and not pregnant.
7. Must provide written informed consent prior to any clinical investigation related procedure.
8. Willing to comply with study evaluation requirements
9. Female subjects of child-bearing potential are required to have a negative pregnancy test done within 7 days prior to the implant procedure per site standard test. Female patients of childbearing potential should be instructed to use safe contraception (e.g., intrauterine devices, hormonal contraceptives: contraceptive pills, implants, transdermal patches hormonal vaginal devices, injections with prolonged release.)

Exclusion Criteria:

1. Patients have non-specific intraventricular conduction delay or right bundle branch block
2. Previously implanted cardiac devices with three or more permanent leads
3. History of aortic valve repair or replacement
4. History of tricuspid valve replacement
5. Pregnant or nursing subjects and those who plan pregnancy during the clinical investigation follow-up period.
6. Recent (< 3 months) myocardial infarction, ablation, electrolyte imbalance, or any condition within the last 90 days that would contraindicate for pacemaker or CRT implant in the opinion of the investigator
7. Presence of other anatomic or comorbid conditions, or other medical, social, or psychological conditions that, in the investigator's opinion, could limit the subject's ability to participate in the clinical investigation or to comply with follow-up requirements, or impact the scientific soundness of the clinical investigation results.