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)