Which of the following is NOT an acyanotic congenital heart defect?

• A. Ventricular septal defect
• B. Atrial septal defect
• C. Tetralogy of Fallot
• D. Patent ductus arteriosus

Answer: (C)

Acyanotic versus cyanotic heart defects are distinguished by whether blood oxygenation remains normal or becomes desaturated in the systemic circulation. The first, second, and fourth options typically involve left-to-right shunts (or obstructive lesions that don’t cause desaturation at rest), leading to increased pulmonary blood flow without persistent cyanosis. Tetralogy of Fallot, however, is a cyanotic defect. The combination of a ventricular septal defect with right ventricular outflow tract obstruction often produces a right-to-left shunt, allowing deoxygenated blood to enter the systemic circulation and causing cyanosis (blue spells). That right-to-left component is what makes it not acyanotic. So Tetralogy of Fallot is the cyanotic defect among these choices, while the others are classically acyanotic.