CASE PRESENTATION: A previously healthy 45-year-old man was admitted to our ED with a 3-week history of progressive dyspnea on exertion. He also presented with orthopnea, paroxysmal nocturnal dyspnea, and mild ankle swelling, but he showed no fever, wheezing, coughing, or sputum production. Outpatient laboratory studies, performed 1 week after symptom onset, revealed hypereosinophilia (4.100/mu L). He was diagnosed with asthma and prescribed inhaled corticosteroids and low-dose prednisone, but he showed no symptomatic improvement. Over the last 48 h, he experienced rapid progression of dyspnea that made it difficult to speak with accompanying resting, substernal, nonradiating chest pain that became worse on inspiration. He had no allergies and reported no recent travels. Before symptom onset, he had not been taking any medication. He denied eating raw fish or meat and had not been exposed to mildew. His only exposure to animals was from his two indoor cats.