The thymus is known to be the site of T cell development in humans. Due to its location in the chest in front of the heart, incidental thymecomy is commonly performed during cardiothoracic surgery, especially in infants and children, so that surgeons may gain access to the surgical field. This practice has been considered safe because it was thought that the thymus is inactive after birth. However, recent data using newly developed techniques has demonstrated that the thymus normally is active well into adulthood. In addition, in a previous study (UCLA IRB # 02-03-008-02) we have demonstrated alterations in lymphocyte (T cells) number in individuals who have undergone thymectomy in childhood but we do not know how immunity is affected. We plan to investigate if immune development or immune function later in life is affected by the loss of T cell production caused by thymectomy during cardiothoracic surgical procedures in childhood. At UCLA, a large number of patients are seen who have congenital heart disease and undergo surgical procedures for correction or repair and many children and adults are followed for many years after they have undergone surgical procedures. Subjects for study will be recruited from among these patients.

We propose a study which will examine the number and activity of lymphocytes obtained from blood samples from child and young adult subjects who have undergone surgery in early childhood. We will determine if these subjects have had complete thymectomy in the past using CT or MRI (obtained during routine care) or, for subjects who are having cardiothoracic surgery, by visualization of thymic tissue during the procedure. In addition we will give vaccination for a common viral illness (hepatitis A) and measure immune responses to it (from a blood sample). As part of this study, we will ask for medical information consisting of a history of congenital cardiac disease and other diagnoses (such as asthma), a history of infections and hospitalizations, and information about immunizations. We will also ask about a list of specific symptoms which will give us information about the function of the immune system.

Inclusion Criteria:

• Age: birth to 35 years.
• Planning cardiac surgical procedure at UCLA Medical Center.
• For subjects with a history of prior cardiothoracic surgery: undergoing CT or MRI evaluation prior to reoperation.

Exclusion Criteria:

• Unable to travel to UCLA Medical Center for follow up blood tests (infants and young children in longitudinal study)
• Known thymus/immune deficiency disorder (i.e. DiGeorge Syndrome)

child and young adult subjects who have undergone surgery in early childhood for correction or repair related to congenital heart disease enrolled for the observational portion of this protocol only