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

• 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].