Veterinary Heart Murmur Grading (Levine 1-6 Scale)
The Levine 1-6 grading scale is the standard veterinary murmur intensity scale. Tap each grade for a description, thrill notes, and clinical implications.
Tap a grade for clinical detail
Tap a grade above to see the description, thrill notes, and clinical implications.
How to use this tool
The 1-6 scale at a glance
1/6 = barely audible, often only after focused listening. 2/6 = soft, readily heard. 3/6 = moderate intensity, similar to heart sounds. 4/6 = loud, no thrill. 5/6 = loud + palpable thrill. 6/6 = audible with stethoscope off the chest wall, palpable thrill.
Why thrill matters
A palpable precordial thrill (best felt at the point of maximal intensity) is the dividing line between grade 4 and grade 5. Practically: thrill = severe enough to feel through the chest wall.
Innocent vs pathologic murmurs
In puppies/kittens under ~4 months, soft grade 1-2 left basilar murmurs are often physiologic (functional / innocent) and resolve by 4 months. Persistence beyond that, or any murmur in an adult, warrants echocardiogram.
Murmur character and timing
Document where loudest (point of maximal intensity), character (plateau, crescendo-decrescendo, machinery), and timing (systolic, diastolic, continuous). Mitral regurgitation: holosystolic apical left. Aortic stenosis: crescendo-decrescendo systolic left base radiating to the carotids. PDA: continuous "machinery" murmur at left heart base.
Frequently asked questions
What is the difference between a grade 4 and a grade 5 murmur?
The presence of a palpable precordial thrill. Grade 4: loud, easily heard, NO palpable thrill. Grade 5: loud PLUS a palpable thrill at the point of maximal intensity. Practically, if you can feel the murmur through the chest wall, it's grade 5 or 6.
Is a grade 2 murmur in a puppy normal?
Often yes - soft grade 1-2 left basilar murmurs in puppies under ~4 months are commonly "innocent" or physiologic and resolve by 4 months of age. Persistence beyond 4 months, or any murmur in an adult, warrants echocardiogram.
When should I refer for echocardiogram?
Any grade 3+ murmur in an adult dog. Any murmur in a cat > 2 years (cat murmurs correlate poorly with disease severity - need echo to characterise). Puppy/kitten murmurs that persist past 4 months.