To determine feasibility of recruitment and tolerability of treatment with sacubitril-valsartan among adult age survivors of cancer diagnosed at or before age 39 who have stage B heart failure.

The current study will test the hypothesis that among adult age survivors of cancer diagnosed at age < 39 years treatment of Stage B heart failure with sacubitril-valsartan is feasible and safe.

Inclusion Criteria:

• Age </= 39 years old at time of cancer diagnosis
• Clinical records adequate to determine diagnosis and treatment regimen
• Previous anthracycline chemotherapy
• Global longitudinal strain <18% and/or
• Left ventricular ejection fraction (LVEF) below the institutional lower limit of normal but >/=40% on echocardiogram or cardiac magnetic resonance imaging (MRI)
• No symptoms of heart failure (shortness of breath, fatigue, swelling). Ordinary physical activity does not cause undue fatigue, palpitation, dyspnea (shortness of breath).

Exclusion Criteria:

• -Age <18 years
• Inability to obtain consent from patient or legally authorized representative
• Active acute or chronic psychiatric illness that in the opinion of the investigator may prevent compliance with study instructions
• Limited English or Spanish proficiency that in the opinion of the investigator may prevent understanding the content of the informed consent form or safely completing the study procedures
• Participation in another concurrent intervention study within 30 days or treatment with an investigational drug within 5 half-lives prior to randomization
• Greater than mild mitral or aortic valve regurgitation/stenosis known pre-cancer therapy
• Severe kidney disease (glomerular filtration rate (GFR) <30 milliliters (mL)/minute (min)/1.73 meters squared (m2))
• Chronic hyperkalemia (>5millimoles per liter (mmol/L))
• Evidence of Coronavirus (COVID-19) within the last 60 days or recent (21 days) exposure to close personal contact with COVID-19.
• Greater than moderate tricuspid or pulmonary valve regurgitation/stenosis known pre-cancer therapy
• Hemodynamically significant congenital heart disease in the opinion of the investigator (not including patent foramen ovale (PFO)/small atrial septal defect (ASD) or small ventricular septal defect (VSD))
• Greater than moderate pericardial effusion
• Constrictive cardiomyopathy diagnosed pre-cancer therapy
• Family history of genetic cardiomyopathy
• Evidence of infiltrative cardiomyopathy
• Symptomatic heart disease based on New York Heart Association (NYHA) classification
• Allergy to valsartan or sacubitril
• Inability to complete cardiac magnetic resonance (CMR) or 6-minute walk test
• Inability to measure non-invasive blood pressure and heart rate in the ambulatory/home setting
• Pregnant/lactating
• History of severe hypersensitivity reactions to gadolinium-based contrast agents (will perform limited cardiac imaging without contrast)
• Concomitant use of other angiotensin-converting enzyme (ACE) inhibitors or angiotensin II receptor blockers (ARBs), aliskiren, non-steroidal anti-inflammatories (NSAIDs) or lithium or the inability to stop these medications for the study

There are no plans to make individual participant data available to other researchers at this time.

Cardiac magnetic resonance studies will be de-identified and assigned a study number. The identification key will not be available to cardiac magnetic resonance readers so that they are blinded to treatment allocation