Which condition is most likely if a heart murmur is categorized as "loud with thrill"?

A heart murmur that is categorized as "loud with thrill" indicates a higher intensity murmur, which typically corresponds to a Grade 4 murmur. Murmurs are graded on a scale from 1 to 6 based on their intensity, with Grade 1 being very faint and Grade 6 being the loudest, audible without a stethoscope.

A Grade 4 murmur is characterized as loud enough to be heard clearly with a stethoscope but is also associated with a palpable thrill, which is a vibration you can feel on the chest wall. This palpable thrill suggests significant turbulence in blood flow, often associated with more severe heart valve abnormalities, shunting, or other conditions causing increased blood flow or disturbances.

In this context, while Grade 5 and Grade 6 murmurs are also loud, they either represent even greater intensity or are audible without a stethoscope, and that involves characteristics beyond just being loud with a thrill. Therefore, the correct categorization for a murmur described as "loud with thrill" is indeed Grade 4.