There are many kids born with congenital heart disease. Some of these defects may lead to the formation of a single ventricle (the heart having only one pumping chamber). These children normally undergo a series of corrective surgeries to help overcome the problems of having just one ventricle. However there are some differences in how well the patients respond to the surgeries. In the adult population, studies have shown that there may be a genetic link that may be responsible for the differences in how patients respond. The investigators would like to study the pediatric population by looking for certain genetic markers in the patients' blood. They will also collect basic health information on each patient.