Safety and Tolerability Study of XXB750 in Heart Failure Participants With Reduced or Mildly Reduced Ejection Fraction (HFrEF/HFmrEF)

Key Inclusion Criteria: * NYHA functional class II-III * LVEF ≤ 50% documented at screening * Systolic blood pressure 110 - 160 mmHg (cohort 1) or 105-160 mmHg (cohort 2), and heart rate between 50-90 beats per minute, inclusive * Treatment with a stable dose of a beta blocker. * Cohort 1: Treatment with a stable dose of ACE inhibitor or ARB * Cohort 2: Treatment with a stable dose of sacubitril/valsartan. Key Exclusion Criteria * Acute decompensated heart failure within 3 months prior to screening. Acute coronary syndrome, stroke, transient ischemic attack, cardiac, carotid, or other major cardiovascular surgery, PCI, or carotid angioplasty within the 6 months prior to screening * Hemodynamically significant mitral and/or aortic valve disease, except mitral regurgitation secondary to LV dilatation at screening * Implantation of a CRT device within 3 months prior to screening or intent to implant a CRT during the study period * History of severe pulmonary disease (e.g. COPD) requiring chronic supplemental oxygen therapy or pulmonary hypertension requiring pharmacology treatment at Screening * eGFR \<45 mL/min/1.73 m2 at screening * Cohort 1 only: Treatment with sacubitril/valsartan currently or within 4 weeks from screening * Cohort 2: Treatment with ACE inhibitor or ARB currently or within 4 weeks from screening * BMI \>40 kg/m2 Other protocol-specific criteria may apply.