A 29-year-old woman was found to have clinical and biochemical evidence of a functioning paraganglioma (pheochromocytoma) five years after the onset of symptoms. Despite extensive investigation of known potential sites of paragangliomas (including laparatomy), the suspected tumor eluded localization. Adrenergic blocking agents controlled her blood pressure but did not affect the other manifestations of catecholamine excess. Ischemic perforation of the colon and refractory gram-negative sepsis resulted in death. At autopsy, a large paraganglioma was found within the heart; the unique tumor location was an important factor in the fatal clinical course.