In which congenital heart defect are the great vessels described as arising in parallel from the base of the heart?

• A. Transposition of the great vessels
• B. Tetralogy of Fallot
• C. Truncus arteriosus
• D. Hypoplastic left heart

Answer: (A)

The key idea is how the great vessels originate from the heart. In this defect, the great arteries arise in parallel from the base of the heart, not in the normal sequence. Specifically, the aorta comes off the right ventricle and the pulmonary artery comes off the left ventricle. This creates two separate, parallel circulations: systemic and pulmonary, rather than a single, connected series circuit. Survival relies on some mixing between the circuits (for example, via a patent foramen ovale/ASD, a VSD, or a PDA).

On imaging or exam notes, this parallel arrangement is the hallmark of transposition of the great vessels. The other defects mentioned involve different relationships or groupings of the outflow tracts: tetralogy of Fallot features a VSD with an overriding aorta and outflow obstruction; truncus arteriosus has a single arterial trunk supplying both systems; hypoplastic left heart involves underdevelopment of the left-sided structures rather than parallel great vessel origins.