Accounting for almost 50% of congenital heart defects, which is the most common congenital heart defect?

• A. Tetralogy of Fallot
• B. Ventricular Septal Defect
• C. Patent Ductus Arteriosus
• D. Transposition of the Great Arteries

Answer: (B)

Ventricular septal defect is the most common congenital heart defect. It occurs when the wall between the left and right ventricles doesn’t form completely, leaving a hole through which blood from the higher-pressure left ventricle shunts to the right ventricle (a left-to-right shunt). Because this defect is so prevalent, many cases are detected early, and small defects often close on their own as the child grows, sometimes within the first year of life.

Clinically, small VSDs may be barely hemodynamically significant, while larger ones increase pulmonary blood flow, leading to rapid breathing, feeding difficulties, poor weight gain, and signs of congestive heart failure in infancy. On examination you may hear a harsh holosystolic murmur best heard along the left lower sternal border, with a possible thrill; chest X-ray can show increased pulmonary markings due to overcirculation.

Other defects listed—Tetralogy of Fallot, patent ductus arteriosus, and transposition of the great arteries—are less common overall and have distinct clinical pictures and management. Thus, the diaphragm is between most CHDs and the characteristic, typical presentation aligns with a ventricular septal defect, making it the best answer here.