A 61-year-old woman presented to the emergency department after experiencing palpitations, shortness of breath, and syncope while taking a shower. Her husband revived her with mouth-to-mouth resuscitation. She had had a similar episode three days earlier while making her bed and had lost consciousness for about 10 sec. She did not appear to have had a seizure. Five months earlier, while taking a walk, she had experienced dizziness, dyspnea, and chest pressure lasting about an hour. A workup at that time included cardiac catheterization, lung scanning, and esophagogastroduodenoscopy, but no abnormality was found. Lower extremity edema was noted.