A 75-year-old man was evaluated in consultation for dyspnea. He was admitted to the hospital 1 day earlier with chest pain and progressive dyspnea over 12 months, which was mild with exertion but worse when he lay flat. He noted increasing daytime fatigue over the same time period. He had been able to work until recently as a building maintenance man. After hospital admission, he underwent cardiac catheterization, which showed no evidence of coronary artery disease. A sudden worsening of dyspnea developed, however, while he was lying supine at the end of the procedure.