A 4-year-old child has a new grade II vibratory, mid-systolic murmur at the mid-sternal border that is louder when the child is supine. What is the most likely diagnosis?

A 4-year-old child has a new grade II vibratory, mid-systolic murmur at the mid-sternal border that is louder when the child is supine. What is the most likely diagnosis?

• A. Pathologic murmur
• B. Pulmonary flow murmur
• C. Still's murmur
• D. Venous hum

Answer: (C)

The key idea is recognizing an innocent pediatric murmur by its quality, location, and how it changes with position. This description matches Still’s murmur: a soft, vibratory or musical murmur heard in early to mid-systole, best along the left lower sternal border, typically grade II, and often louder when the child is lying supine. In a healthy 4-year-old, this pattern is classic and reassuring because it is positional (louder when supine) and diminishes with age or when the child sits/stands. The lack of harshness, radiation, or diastolic component argues against a pathologic murmur or a venous hum, and the location at the mid-sternal border with a vibratory quality fits Still’s murmur best.

The key idea is recognizing an innocent pediatric murmur by its quality, location, and how it changes with position. This description matches Still’s murmur: a soft, vibratory or musical murmur heard in early to mid-systole, best along the left lower sternal border, typically grade II, and often louder when the child is lying supine. In a healthy 4-year-old, this pattern is classic and reassuring because it is positional (louder when supine) and diminishes with age or when the child sits/stands. The lack of harshness, radiation, or diastolic component argues against a pathologic murmur or a venous hum, and the location at the mid-sternal border with a vibratory quality fits Still’s murmur best.