Background: It is well known that atrial fibrillation (AF) patients not receiving anticoagulants are at higher risk of Ischemic Stroke (IS).Objective: Our objective is to estimate how much the Medicare program spends during one-year treating a Medicare beneficiary (MB) with AF who were not being anticoagulated prior to or during their IS hospitalization.Methods: This cross-sectional study population consisted of all MBs in the fee-for-service program who were discharged from a hospitalization for IS having AF during 2018. Patients were excluded for a prior history of stroke or already receiving long-term anticoagulants. Medicare spending was defined as paid claims during the index hospitalization and all facility claims that began within 12-months of the index hospital discharge date even if admission occurred in 2019.Results: The final sample was 50,509 MBs. Average Medicare Part A spending per beneficiary was $46,867 +/- $49,212, for a total of nearly $2.5 billion. Highest average spending per MB was for hospital services $25,848, of which $15,790 +/- $20,984 occurred during the index hospitalization, and $10,058 +/- $21,956 for rehospitalization. The Medicare program average MB spending included $8131 +/- $14,979 at skilled nursing facilities, $5538 +/- $12,739 at rehabilitation facilities, and $3056 +/- $7495 for outpatient facilities or emergency departments.Conclusion: MBs with AF who are not treated with anticoagulants and then suffer an ischemic stroke result in one-year Medicare Part A program spending of approximately $47,000 per person compared to an average spending of approximately $12,800 per beneficiary in the Medicare program in 2018 [1]. Identification and anticoagulation treatment in AF could result in significant healthcare savings.