The Comparative Effectiveness Between ARNI and ACE Inhibitor/ARB Medication in Patient With HFrEF

Inclusion Criteria: * HF patients were defined as those with "heart failure" according to the disease code in the main code and the sub-code in the claims data. HF patients who were assigned the following KCD-6 disease codes were considered as: "hypertensive heart disease with (congestive) HF" (I11.0), "hypertensive heart and renal disease with (congestive) HF" (I13.0), "hypertensive heart and renal disease with both (congestive) HF and renal failure" (I13.2), and "HF" (I50) including "congestive HF" (I50.0), "LV failure" (I50.1), and "HF and unspecified" (I50.9). * HFrEF patients were defined with the following KCD-6 disease codes: "Congestive heart failure with systolic dysfunction"(I5004), "Left ventricular failure"(I501), "Ischaemic cardiomyopathy"(I22.5), "Dilated cardiomyopathy" (I420). Hospitalized heart failure is defined as the HF disease code and admission. Exclusion Criteria: * Less than 18 years old * In case where investigators determine it's inappropriate to be included in the study as per investigators' clinical judgment