Which murmur is characterized by non-radiating sounds at the apex?

The murmur characterized by non-radiating sounds at the apex is associated with mitral stenosis. In this condition, the mitral valve is narrowed, which impedes blood flow from the left atrium to the left ventricle during diastole. The characteristic sound produced is a low-pitched, rumbling diastolic murmur best heard at the apex of the heart, often with the patient in the left lateral position.

This murmur typically does not radiate to other areas, which distinguishes it from murmurs associated with other conditions. For instance, aortic stenosis would typically present with a systolic ejection murmur that can be heard radiating to the carotids, while pulmonic regurgitation is more often associated with a diastolic murmur that can be heard along the left sternal border rather than the apex. A ventricular septal defect usually produces a holosystolic murmur best heard at the left sternal border, again not at the apex and typically with radiation to the right.

Thus, the defining feature of a non-radiating apex murmur aligns specifically with mitral stenosis, making it the correct answer in this context.