The case of a patient with an intracardiac ectopic thyroid is reported. A lesion was found in a 25-year-old man and was diagnosed by two-dimensional echocardiography as a right intraventricular tumor. An operation was performed. Histologic and ultrastructural studies showed that the tumor was a thyroid mass. The origin of intracardiac ectopic thyroids is probably to be found in disturbances occurring early in embryogenesis.