Case Presentation: A 70-year-old woman was transferred to our ED from an outside ED for hypoxemia. Three weeks earlier, an inpatient evaluation for syncope revealed a right intraventricular filling defect, multiple pulmonary nodules, pulmonary emboli, and a left breast mass. She underwent breast biopsy, was started on rivaroxaban, and was discharged with outpatient follow-up. She experienced progressively worsening dyspnea, prompting a return to the outside ED, where she was found to be severely hypoxemic and was intubated. Her medical history included diabetes, hypertension, hyperlipidemia, COPD, hypothyroidism, diastolic heart failure, and a 40+ pack-year smoking history., (Copyright © 2021 American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.)