Congenital heart disease (CHD) has been defined as “. . . a gross structural abnormality of the heart or intrathoracic great vessels that is actually or potentially of functional significance” (Mitchell, Korones, and Berendes 1971). Congenital heart disease is the most common single group of congenital abnormalities, accounting for about 30% of the total. The incidence is reported as varying between 0.3% and 1% of all live births. Ten to 15% of children with congenital heart defects have more than one cardiac abnormality; up to one-third also have one or more associated noncardiac congenital abnormalities (Wernovsky 2006). Although some forms of CHD are minor and do not require any medical or surgical intervention, others are very complex and may necessitate a series of staged surgical procedures and/or require life-long medications. Significant improvements in medical and surgical techniques have resulted in increasing numbers of children and adults living with CHD, and it is currently anticipated that 80%–85% of children born with CHD today will survive into adulthood (British Cardiac Society 2002). However, although survival rates have improved dramatically over the last 40 years or so, morbidity remains a concern. Congenital heart defects can be broadly subdivided into two groups, based on changes in the circulation. Acyanotic defects may be due to either a left-to-right shunt or to an obstructive lesion; there is no mixing of desaturated blood in the systemic arterial circulation. With cyanotic defects, there may be either increased or diminished pulmonary flow, and desaturated blood enters the systemic arterial circulation, regardless of whether cyanosis is clinically evident. Unsaturated venous blood bypassing the lungs can result in secondary polycythemia, which is a compensatory mechanism to carry more oxygen to the tissues. This causes increased viscosity, which in turn results in sluggish blood circulation and impeded blood flow, particularly in the capillaries. Poor peripheral blood flow and clubbing of the fingers and toes can result, breathlessness and fatigue often result in a reduced exercise tolerance, and growth may be affected.