Omecamtiv Mecarbil for Severe Heart Failure

Inclusion Criteria: Adult patients who meet all the following criteria at screening may be included in the study: * Are between ≥ 18 years and ≤ 85 years at the signing of informed consent * Have a history of chronic HFrEF, defined as requiring treatment for HF for a minimum of 3 months prior to screening * Are receiving oral loop diuretics on a regular schedule * Patients without AFF on screening ECG: * LVEF \< 30% within 6 months of screening * Elevated N-terminal prohormone of B-type natriuretic peptide (NT-proBNP) ≥ 1000 pg/mL (BNP ≥ 300 pg/mL) * Patients with AFF on screening ECG: * LVEF \< 25% within 6 months of screening * Elevated N-terminal prohormone of B-type natriuretic peptide (NT-proBNP) ≥ 3000 pg/mL (BNP ≥ 900 pg/mL) * Not currently taking digoxin * Meet one of the following criteria for a recent HF event: * Are currently hospitalized with the primary reason of HF * Had an HF event (as defined in the primary endpoint) within 12 months prior to screening. For the purposes of a qualifying HF event, subcutaneous furosemide will be treated as equivalent to intravenous furosemide Or * Had outpatient escalation of oral diuretics due to worsening signs and symptoms of heart failure plus one of two additional criteria sustained for at least 1 week: (1) at least 50% or 1.5-fold increase in daily loop-diuretic-equivalent dose; (2) the addition of a new diuretic class to a loop diuretic. * Are established on regional standard-of-care HF therapies for at least 30 days prior to screening * Systolic blood pressure ≤ 140 mmHg Exclusion Criteria: Any of the following criteria will exclude potential patients from the study: * Have AFF on the screening ECG and are currently taking digoxin * Have had any event or procedure that may have resulted in a change in ejection fraction, including, but not limited to, acute coronary syndrome and/or any coronary revascularization, cardiac surgery, valve surgery, any coronary revascularization, and/or cardiac resynchronization, or cardiac contractility modulation therapy within 3 months of screening * Are admitted to a long-term care facility or hospice * Have a projected survival of \< 12 months due to non-cardiovascular causes based on clinical judgment * Are receiving intravenous inotropes or intravenous vasopressors ≤ 3 days prior to screening * Are receiving mechanical hemodynamic support or mechanical ventilation ≤ 7 days prior to screening * Are receiving intravenous diuretics, intravenous vasodilators, or supplemental oxygen therapy ≤ 12 hours prior to screening (except for nocturnal supplemental oxygen for sleep apnea or heart failure) * Have an estimated glomerular filtration rate (eGFR) \< 20 mL/min/1.73m2 or receiving dialysis at screening * Have previously had a solid organ transplant * Are receiving treatment in another investigational device or drug study or are within 30 days of ending such investigational treatment at screening * Have received omecamtiv mecarbil in a previous clinical trial * Are pregnant or planning pregnancy during the study period, or planning to breastfeed during treatment with IP or within 5 days after the end of treatment with IP * Have primary infiltrative cardiomyopathy (e.g. cardiac amyloidosis) or severe stenotic valvular disease