While cardiac resynchronization therapy remains the mainstay for advanced HF, it is not always feasible due to unfavorable anatomy of coronary sinus or pacing characteristics. In such cases, left bundle branch area pacing itself or left bundle optimized cardiac resynchronization therapy could be a rescue therapy for failed or unsuccessful biventricular cardiac resynchronization therapy. However, the efficacy and safety of left bundle branch area pacing (or left bundle optimized cardiac resynchronization therapy) as rescue therapy for biventricular cardiac resynchronization therapy is largely hypothetic and lack concrete evidence still. Therefore, there is an unmet need for the registry purposed for left bundle branch area pacing among heart failure with mid-range (or mildly reduced) ejection fraction and heart failure with reduced ejection fraction patients to investigate its efficacy and safety. This study aims to investigate the efficacy and safety of left bundle branch area pacing in heart failure patients with ejection fraction below normal using Selectra catheters.