A 67-year-old woman presented to the ED with progressive dyspnea of 2 weeks duration, which had worsened over the previous day, and was associated with pleuritic chest pain and palpitations. There were no associated fever, chills, cough, hemoptysis, dizziness, syncope, nausea, vomiting, or lower extremity edema. She had been hospitalized recently for the evaluation of dyspnea and was found to have pulmonary hypertension and atrial fibrillation, for which she was receiving therapy with warfarin. Her medical history was significant for adenocarcinoma of the right breast diagnosed in 1997, which was treated with a right mastectomy followed by chemotherapy with tamoxifen and letrozole. The patient had no history of smoking, alcohol abuse, or illicit drug use. Her family history was noncontributory. There was no history of recent travel. Her medications included letrozole, atenolol, spironolactone, warfarin, furosemide, and simvastatin.