PET scan or Positron Emission Tomography is an advanced form of an X-ray. It is used to detect radioactive substances in the body. During this study researchers plan to inject small amounts of the radioactive drug fluorodopamine into patients. Fluorodopamine is very similar to the chemicals found in the sympathetic nervous system. It can attach to sympathetic nerve endings and allow researchers to view them with the aid of a PET scan. One area of the body with many sympathetic nerve endings is the heart. After giving a dose of fluorodopamine, researchers will be able to visualize all of the sympathetic nerve endings involved in the activity of the heart. In addition, this diagnostic test will help researchers detect abnormalities of the nervous system of patient's hearts.