Case Presentation: A middle-aged man with a history of heart failure and atrial fibrillation presented to the hospital with subacutely worsening dyspnea. He had hypoxemia, crackles on pulmonary auscultation, and diffuse airspace opacities on chest radiograph. Admission was requested for presumed exacerbation of heart failure. Upon closer examination, he no edema or elevated jugular venous [...]