Which defect is characterized by a harsh murmur heard at the left sternal border?

A ventricular septal defect (VSD) is characterized by a harsh murmur that is typically heard at the left sternal border. This is due to the flow of blood from the left ventricle, where the pressure is higher, into the right ventricle through the opening in the septum. The turbulence created as the blood passes through this defect is what results in the characteristic harsh sound.

In VSD, the murmur is often described as being "holosystolic" or "pan-systolic," which means it occurs throughout the entire systolic phase of the cardiac cycle. It is important to recognize this type of murmur, as it is a key clinical finding that can help in diagnosing the condition.

In contrast, other defects have different characteristics. An atrial septal defect (ASD) typically produces a softer murmur and may also have a fixed split S2 sound. The murmur associated with a patent ductus arteriosus (PDA) is usually continuous and can be heard throughout the cardiac cycle. Coarctation of the aorta does not prominently present with a murmur at the left sternal border but may be associated with other findings such as differential blood pressures in the limbs.