Which of the following best describes a grade 3 heart murmur?

A grade 3 heart murmur is best described as being moderately loud. This level of murmur can be heard with a stethoscope placed on the chest and is characterized by a volume that is greater than a grade 2 murmur but less than a grade 4 murmur.

To provide further context, murmurs are classified on a scale from 1 to 6, with grade 1 being very faint and grade 6 being audible without a stethoscope (i.e., audibly heard by the naked ear). The definitions of the grades help clinicians ascertain the potential significance of the murmur.

Grade 3 murmurs, while noticeable and audible, do not typically produce the vibrations or "thrills" associated with more intense murmurs. The presence of a thrill indicates a higher grade (specifically grade 4 or above), where the turbulence from the blood flow creates palpable vibrations. Therefore, the description of a grade 3 murmur as moderately loud is precise, reflecting its position in the grading scale.