What characterizes a holosystolic murmur best heard in the left lower sternal border?

• A. Atrial septal defect
• B. Mitral regurgitation
• C. Ventricular septal defect
• D. Aortic stenosis

Answer: (C)

A holosystolic murmur, which occurs throughout the entire systole, is characterized by its continuous sound that begins with the first heart sound and continues until the second heart sound. When this type of murmur is best heard at the left lower sternal border, it is typically associated with conditions involving a shunt between the ventricles or a significant regurgitant flow.

In particular, a ventricular septal defect leads to the abnormal flow of blood from the left ventricle to the right ventricle due to the presence of an opening in the septum that separates the two ventricles. This left-to-right shunting causes a holosystolic murmur because the pressure in the left ventricle is higher during systole, resulting in a continuous turbulent flow of blood through the defect. This murmur tends to be loudest at the left lower sternal border due to the proximity of the defect to the chest wall and the direction of flow.

In contrast, murmurs associated with conditions such as mitral regurgitation can also present as holosystolic but are typically better heard at the apex of the heart, while conditions like aortic stenosis present as systolic "ejection" murmurs that start after the