The murmur described as holosystolic and loudest at the left lower sternal border is most characteristic of which defect?

• A. At the left upper sternal border
• B. At the left lower sternal border
• C. At the apex
• D. At the right lower sternal border

Answer: (B)

A holosystolic murmur heard best at the left lower sternal border is classic for a ventricular septal defect. This defect allows blood to flow from the left ventricle to the right ventricle throughout systole, producing a harsh, continuous murmur that is most conspicuous at the LLSB where the right-sided septal contact is greatest. The murmur’s intensity often reflects the defect size—smaller defects generate a louder murmur due to a higher pressure gradient, while larger defects can be softer despite more shunting. If the murmur were best heard at the apex, mitral regurgitation would be more likely, and a murmur best at the left upper sternal border would point toward other lesions not typical of a VSD.