A Study to Learn More About How Safe Finerenone is, When it is Taken for a Longer Time With Standard Treatment, in Children and Young Adults With Heart Failure and Left Ventricular Systolic Dysfunction

Inclusion Criteria: * For participants rolling over from randomized controlled trial (RCT): Prior participation in the finerenone Phase 3 study FIORE (21466) and not permanently discontinued from the study intervention prior to the end of treatment (EoT) visit in FIORE. * For newly enrolled infants \<6 months of age: Left ventricular systolic dysfunction (LVSD) with left ventricular ejection fraction (LVEF) ≤ 50% at screening assessed by echocardiography. * For newly enrolled infants \<6 months of age: Elevated NT-pro BNP levels (\> 500 ng/L) at screening. * For newly enrolled infants \<6 months of age: Heart failure (HF) etiologies include congenital heart defects (CHD) with biventricular physiology and systemic LV; idiopathic cardiomyopathy (CM); familial/inherited and/or genetic CM; history of myocarditis (diagnosis of an acute episode at least 3 months prior to treatment assignment); neuromuscular disorder; inborn error of metabolism; mitochondrial disorder; acquired (chemotherapy, iatrogenic, infection, rheumatic, or nutritional); ischemic (e.g., Kawasaki disease and postoperative HF); LV noncompaction. * For newly enrolled infants \<6 months of age: Receiving standard of care (SoC) treatment for heart failure according to local guidelines or investigator´s discretion (on a stable regimen for 30 days before baseline). * Newly enrolled newborns and infants \< 6 months of age must have a body weight of ≥3 kg at Visit 1. Exclusion Criteria: * For participants rolling over from randomized controlled trial (RCT): To roll-over to FIORELLO, all participants: Potassium (K+) \>5.5 mmol/L based on local laboratory results. After unblinding: * For participants who received finerenone in FIORE: K+ \>5.5 mmol/ L * For participants who received placebo in FIORE: K+ \>5.0 mmol/L for children ≥2 years of age, and \>5.3 mmol/L for children \<2 years of age (if eGFR is \<60 mL/min/1.73m² for participants \<2 years of age, the serum potassium threshold of \>5.0 mmol/L will be used for exclusion) * For newly enrolled newborns and infants \< 6 months of age: Potassium ≥ 5.3 mmol/l (if eGFR is \<60 mL/min/1.73m², the serum potassium threshold of \>5.0 mmol/L will be used for exclusion). * For participants rolling over from RCT: Severe renal dysfunction with estimated glomerular filtration rate (eGFR) \< 30 ml/min/1.73m² based on local laboratory results at FIORELLO Visit 1. * For newly enrolled infants \< 6 months of age: Severe renal dysfunction with eGFR \< 30 ml/min/1.73m2 at screening or Visit 1. * Treatment with a mineralocorticoid receptor antagonist, other than the study intervention, (e.g., spironolactone, eplerenone) within 30 days of Visit 1. * Requirement of any intravenous (IV) vasoactive agents; mechanical ventilation; mechanical circulatory support; sustained or symptomatic arrhythmias not controlled by drug or device therapy within 30 days prior to study treatment.