Which statement best describes transposition of the great vessels?

• A. Coarctation of the aorta
• B. Reversal of the aorta and pulmonary artery
• C. Tetralogy of Fallot
• D. Ventricular septal defect

Answer: (B)

The key idea is how the great arteries are connected to the ventricles. In transposition of the great vessels, the aorta arises from the right ventricle and the pulmonary artery arises from the left ventricle, so the systemic and pulmonary circuits run in parallel rather than in series. This reversal creates two closed loops with little mixing unless there is an additional defect (such as a PDA, ASD, or VSD) that allows oxygenated and deoxygenated blood to mix. Clinically, this presents with cyanosis in newborns unless a mixing pathway is present. The other conditions describe different heart defects: coarctation is a narrowing of the aorta, tetralogy of Fallot includes multiple defects including a VSD and right ventricular outflow obstruction, and a ventricular septal defect is simply a hole between the ventricles. The statement that best describes transposition is the reversal of the aorta and pulmonary artery connections.