Which murmur is characterized as harsh, high-pitched, and commonly occurs at the left lower sternal border?

The murmur described as harsh, high-pitched, and typically located at the left lower sternal border is characteristic of a ventricular septal defect (VSD). In a VSD, there is an abnormal opening between the ventricles, which allows for turbulent blood flow from the left ventricle to the right ventricle during systole. This turbulent flow creates a distinctive murmur that is best heard at the left lower sternal border. The harsh quality of the murmur often signifies significant left-to-right shunting, which is common in cases of moderate to large VSDs.

Aortic stenosis is generally associated with a systolic ejection murmur that is usually heard at the right second intercostal space and may radiate to the carotids, so it does not fit the description provided. An atrial septal defect typically produces a mid-systolic murmur, which may be auscultated over the left upper sternal border rather than the left lower sternal border. Pulmonary stenosis also has a characteristic murmur, but it is primarily heard over the left second intercostal space rather than the left lower sternal border. This helps differentiate it from the murmur associated with a ventricular septal defect