This is a case of a 92-year-old female with multiple hospitalizations for dyspnea on exertion and hypoxemia. Her symptoms were initially thought to be secondary to pneumonia, and on subsequent admission, culture-negative endocarditis. A computed tomography (CT) of the chest was remarkable for numerous bilateral lung nodules of varying size, some of which had a cavitary appearance raising concern for septic emboli. While a transthoracic echo was unremarkable, a transesophageal echo found a small 3 mm echodensity at the tip of the right coronary leaflet of the aortic valve and a possible mobile echodensity on the tricuspid valve leaflet. These findings further supported a clinical diagnosis of endocarditis with septic emboli in the lungs. Initial bronchoscopy yielded an unremarkable biopsy and a bronchial alveolar lavage with the growth of Actinomyces odontolyticus . During a subsequent hospitalization, a repeat bronchoscopy with transbronchial biopsy revealed a final diagnosis of invasive pulmonary mucinous adenocarcinoma. This case highlights a unique presentation of mucinous adenocarcinoma of the lung initially masquerading as septic emboli, resulting in a delay in the final diagnosis., Competing Interests: The authors have declared that no competing interests exist., (Copyright © 2023, DeMars et al.)