Transposition of the great arteries (TGA) is a serious congenital heart defect in which the two main arteries leaving the heart (the aorta and the pulmonary artery) are switched from their normal positions. In a normal heart, the aorta arises from the left ventricle and carries oxygenated blood to the body, while the pulmonary artery arises from the right ventricle and carries deoxygenated blood to the lungs. In TGA, these connections are reversed.
This creates two parallel circulations that barely mix: deoxygenated blood from the body circulates continuously through the right heart and back to the body without reaching the lungs, while oxygenated blood from the lungs circulates continuously through the left heart and back to the lungs without reaching the body. Without mixing between these circuits (through a septal defect or patent ductus arteriosus), TGA is incompatible with survival.
TGA is a neonatal emergency requiring urgent surgical correction. The arterial switch operation, performed in the first weeks of life, reconnects the great arteries to the correct ventricles and is the definitive treatment. Outcomes have improved dramatically since the 1980s, and most patients now survive to adulthood. Adults who had the arterial switch operation as infants are monitored lifelong for complications including coronary artery abnormalities, valve dysfunction, and arrhythmia.
Congenitally corrected TGA (ccTGA) is a related but distinct condition in which both the great arteries and the ventricles are transposed, partially correcting the circulation but leaving the morphological right ventricle (less suited to systemic pressures) as the main pumping chamber. This carries its own long-term risks including systemic ventricular failure and heart block.
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