A Research Study Comparing CDR132L With Placebo on the Structure and Function of the Heart in People With Heart Failure With Reduced/Mildly Reduced Ejection Fraction and Left Ventricular Hypertrophy

Inclusion Criteria: * Age 40-84 years (both inclusive) at the time of signing the informed consent. * Documented symptomatic heart failure (HF) diagnosed greater than or equal to (≥) 180 days prior to screening with at least weekly need for oral diuretic treatment, and New York Heart Association class II-III at screening. * Clinically stable and on optimized doses and unchanged drug classes of guideline-directed HF therapy ≥ 45 days prior to randomisation. * Left ventricular ejection fraction (LVEF) less than (\<) 50 percent (%) as assessed by echocardiography at screening, measured by central laboratory. * Left ventricular hypertrophy or left ventricular dilatation assessed by echocardiography at screening measured by central laboratory with any of the following: 1. LVMi greater than (\>)88 g/m\^2 for female participants and \>102 g/m\^2 for male participants using the truncated ellipsoid method. 2. LVMi \>95 g/m\^2 for female participants and \>115 g/m\^2 for male participants, using the linear method (cube formula). 3. Left ventricular end-diastolic diameter indexed to body surface area (LVEDDi) \>3.1 cm/m\^2 for female participants and \>3.0 cm/m\^2 for male participants. * Body mass index 18.5-40 kilogram per meter square (kg/m\^2) (both inclusive) and body weight less than or equal to (≤) 140 kilogram (kg). Body mass index is calculated in the electronic case report form based on height and body weight at the screening visit (visit 1). * N-terminal pro B-type natriuretic peptide (NT-proBNP) ≥ 300 picograms per milliliter (pg/mL); NT-proBNP ≥600 pg/mL if atrial fibrillation/flutter is present at time of screening, measured by central laboratory. Exclusion Criteria: * Estimated Glomerular Filtration Rate (eGFR) less than (\<) 30 milliliter/minute/ 1.73-meter square (mL/min/1.73 m\^2) at time of screening, measured by central laboratory. * Participants with an episode of acute kidney failure or acute kidney injury, at the discretion of the investigator,within 90 days prior to randomisation. * Myocardial infarction, unstable angina pectoris or HF hospitalization within 30 days prior to screening. * Participants receiving intravenous HF medications within 45 days prior to randomisation. * Planned coronary revascularization, pacemaker/cardioverter-defibrillator/cardiac resynchronization therapy (CRT) implantation, ablation of cardiac arrythmias or valve repair/replacement at the time of randomisation. * Stroke or transient ischemic attack within 12 months prior to randomisation. * Participants with potential disruption of the blood-brain barrier (e.g., multiple sclerosis), in the opinion of the investigator. * Known history of severe liver disease and/or alanine aminotransferase or aspartate aminotransferase greater than (\>) 2.5x upper limit of normal at screening, measured by central laboratory. * Known genetic (or highly suspected due to family history) cause of increased cardiac mass (including dilated cardiomyopathy, Fabry disease and likely pathogenic or pathogenic variants within hypertrophic cardiomyopathy (HCM). * Participants with suspected or diagnosed cardiac amyloidosis or sarcoidosis.