Treating Heart Dysfunction Related to Cancer Therapy With Sacubitril/Valsartan

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 * L VEF below the institutional lower limit of normal but \>/=40% on echocardiogram or cardiac 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 (GFR \<30 mL/min/1.73m2) * Chronic hyperkalemia (\>5mmol/L) * Evidence of 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 PFO/small ASD or small 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 NYHA classification * Allergy to valsartan or sacubitril * Inability to complete 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 ACE inhibitors or ARBs, aliskiren, NSAIDs or lithium or the inability to stop these medications for the study