In the PROVe mnemonic for Tetralogy of Fallot, what does the letter O stand for?

• A. Pulmonary Valve Stenosis
• B. Right Ventricular Hypertrophy
• C. Overriding Aorta
• D. Ventricular Septal Defect

Answer: (C)

In Tetralogy of Fallot, the term represented by the O in PROVe is Overriding Aorta. This means the aorta is positioned directly above the ventricular septal defect and receives blood from both ventricles rather than solely from the left ventricle. This abnormal placement, due to anterior deviation of the infundibular septum, allows mixing of oxygen-poor blood into the systemic circulation. When paired with pulmonary stenosis, this creates a right-to-left shunt that contributes to cyanosis. The other features—pulmonary stenosis, right ventricular hypertrophy, and the ventricular septal defect—are the remaining components of the syndrome, but the O specifically points to the aorta’s overriding position over the VSD.