A Study to Assess the Hemodynamic Effects, Safety, Tolerability, and Pharmacokinetics of Intravenous APD418 in Adult Participants With Heart Failure With Reduced Ejection Fraction

Inclusion Criteria: * Advanced chronic Heart Failure with Reduced Ejection Fraction (HFrEF), defined as left ventricular ejection fraction (LVEF) less than or equal to (≤) 35% at Screening, including documented history of HFrEF (LVEF ≤ 35%) for at least 4 months prior to Screening * New York Heart Association Class II-IV * Cardiac index ≤ 2.5 liters per minute per square meter (L/min/m\^2) and pulmonary capillary wedge pressure ≥ 15 millimeters of mercury (mm Hg) at Day 1 * Body mass index 18.0 to 37.0 kilograms per square meter (kg/m\^2), inclusive, and body weight \< 150 kg at Screening and Day 1 Exclusion Criteria: * Hemodynamically unstable at Day 1 or in the opinion of the Investigator likely to progress to becoming hemodynamically unstable during the course of the study * Treated with carvedilol or at a dose higher than a total of 25 milligrams per day any time within 72 hours of Day 1 through the end of the in-clinic observation Post-dose Period. * Receiving any mechanical (respiratory or circulatory) or renal support therapy at Screening or Day 1 * Systolic Blood Pressure ≤ 90 millimeter of mercury (mm Hg) or ≥ 160 mm Hg, or Heart Rate \< 50 beats per minute (bpm) or \> 110 bpm, at Screening or Day 1 * Recently treated with inotropic, intravenous (IV) vasoactive or IV diuretic therapy, or expected to require such therapy with these drugs any time from Day 1 through the end of study conduct.