Murmur Intensity Grading Scale (Levine Grades 1–6)
Cardiac murmurs are graded on a 1-to-6 scale based on their loudness on auscultation, with the presence or absence of a palpable thrill serving as the key clinical anchor. The single most important dividing line is that a thrill appears at grade 4 and above. Critically, murmur intensity does not reliably correlate with the severity of the underlying lesion.
Grades 1 and 2: Soft Murmurs (No Thrill)
Grade 1 is barely audible and heard only under optimal conditions — you often have to listen carefully and specifically for it before it registers. Grade 2 is soft but readily audible, meaning it is heard promptly as soon as the stethoscope is placed. Neither of these grades is associated with any palpable thrill. These are the murmurs most easily missed on a rushed exam and are frequently the ones described as incidental or benign-sounding, though grading alone does not establish benignity.
Grade 3: The Threshold of Loudness (Still No Thrill)
Grade 3 is moderately loud and easily heard, but the defining feature is that there is still no palpable thrill. This makes grade 3 the loudest murmur that lacks a thrill and the immediate step below the thrill threshold. Distinguishing grade 3 from grade 4 rests entirely on palpation — if you cannot feel a thrill, the murmur cannot be graded higher than 3 regardless of how loud it seems.
Grades 4, 5, and 6: Loud Murmurs With a Palpable Thrill
A palpable thrill defines grade 4 and above. Grade 4 is loud with a palpable thrill. Grade 5 is very loud with a thrill and can be heard when the stethoscope is only partially in contact with the chest. Grade 6 is the loudest, audible even without the stethoscope touching the chest at all. On palpation, thrills are the vibratory correlate of these loud (grade 4+) murmurs — a thrill felt at the precordium or PMI signals that the murmur is at least grade 4.
High-yield
- The murmur grading scale runs from 1 (barely audible) to 6 (audible without a stethoscope).
- A palpable thrill is the key threshold: it appears at grade 4 and persists through grades 5 and 6.
- Grade 3 = moderately loud but NO thrill; grade 4 = loud WITH thrill — palpation makes the distinction.
- Grade 5 is audible with the stethoscope only partially on the chest; grade 6 is audible with the stethoscope off the chest.
- Thrills are palpable vibrations from loud murmurs (grade 4 or higher) and can be felt during the precordial exam.
- Murmur intensity does NOT always correlate with lesion severity.
Pitfalls
- Assuming a louder murmur always means more severe disease — in severe AS with LV dysfunction the murmur may soften because the failing LV cannot generate enough flow.
- Assuming a soft murmur excludes a dangerous lesion — in severe acute MR the murmur may be soft because LA pressure rises rapidly and reduces the gradient.
- Grading a loud murmur as grade 4+ without actually palpating for a thrill — the thrill, not perceived loudness, defines grade 4 and above.
- Forgetting that VSD murmur loudness is inversely related to defect size (small defect = loud murmur; large defect = softer, laminar flow), another reminder that intensity misleads about severity.
- Confusing grade 5 (stethoscope partially off chest) with grade 6 (no stethoscope needed at all).
Clinical pearls
- No thrill? The murmur can be at most grade 3.
- Feel a thrill? You are at grade 4 minimum.
- Loudness grades the murmur; it does not grade the disease.
- A thrill palpated at the PMI is the tactile signature of a grade 4+ murmur.
Frequently asked
At which grade does a palpable thrill first appear?
A thrill first appears at grade 4. Grades 4, 5, and 6 all have a palpable thrill, while grades 1 through 3 do not.
How do you distinguish a grade 3 from a grade 4 murmur?
By palpation for a thrill. Grade 3 is moderately loud with no thrill; grade 4 is loud with a palpable thrill. Loudness perception alone is not sufficient — you must feel for the thrill.
What defines a grade 6 murmur versus a grade 5?
A grade 6 murmur is audible without the stethoscope touching the chest at all. A grade 5 murmur is very loud with a thrill and is audible when the stethoscope is only partially off the chest.
Does a louder murmur mean more severe valvular disease?
No. Murmur intensity does not always correlate with severity. In severe AS with LV dysfunction the murmur can become softer, and in severe acute MR the murmur may be soft because LA pressure rises rapidly and reduces the gradient.
How would you describe a grade 1 murmur?
Barely audible, heard only under optimal listening conditions. It is the softest grade and easily missed.
What is a thrill and how does it relate to the grading scale?
A thrill is a palpable vibration on the precordium produced by a loud murmur. Its presence indicates a murmur of grade 4 or higher.
Why can a small VSD produce a louder murmur than a large one?
Murmur loudness is inversely related to VSD size — a small defect creates turbulent flow and a loud murmur, while a large defect allows more laminar flow and a softer murmur. This illustrates that intensity does not track with severity.
Turn this into reasoning you can use on exam day — practice Murmur Intensity Grading Scale on branching cases where your decisions shape the patient.