A Study to Assess the Effect of Danicamtiv on the Drug Levels of Midazolam in Participants With Stable Heart Failure

Inclusion Criteria: Ambulatory participants with stable HFrEF due to any etiology. Body mass index (BMI) of 18.0 kilogram per square meter (kg/m2) to 35.0 kg/m2 inclusive. Documented left ventricular ejection fraction (LVEF) 15% to 45% (on 2 occasions), including at least once during Screening and confirmed by the Echo Core Laboratory (the absolute difference between the 2 LVEF values qualifying the participant should be < 12%). Participant receiving chronic medication for the treatment of heart failure reflecting current guidelines, including at least one of the following, unless not tolerated or contraindicated:β-blocker, angiotensin converting enzyme inhibitor, angiotensin receptor blocker, or angiotensin receptor neprilysin inhibitor. Such treatments should have been given at stable doses for at least ≥ 2 weeks prior to screening with no plan to modify treatments during the study. Sinus rhythm or stable atrial or ventricular pacing or persistent atrial fibrillation that is adequately rate-controlled to allow pharmacodynamic (PD) assessments by Transthoracic echocardiogram (TTE). NOTE: Participants with implanted cardioverter defibrillator (ICD), pacing, or cardiac resynchronization therapy are eligible provided device programming is unchanged starting 2 months prior to and throughout the dosing period. Adequate acoustic windows, determined by the Echo Core Laboratory, to enable accurate TTE assessments. Exclusion Criteria: Presence of disqualifying cardiac rhythms that would preclude echocardiographic assessments, as determined by the Investigator, including: (a) rapid, inadequately rate controlled atrial fibrillation or (b) frequent premature ventricular contractions that might interfere with reliable echocardiographic measurements of left ventricular function. History of bronchospasm, or history of respiratory depression or arrest, airway obstruction, oxygen desaturation, or apnea. History of allergy to midazolam, other benzodiazepines, danicamtiv, related compounds, or excipients in the formulations. Severe renal insufficiency (defined as current estimated glomerular filtration rate [eGFR] < 30 mL/min/1.73 m2 by simplified Modification of Diet in Renal Disease equation [sMDRD].