Heart Murmur Grades in Dogs and Cats (I–VI Scale)

What Is a Heart Murmur Grade?

A heart murmur is an abnormal sound produced by turbulent blood flow, heard on auscultation. Grading is simply a standardized way to describe how loud that sound is — and whether it can be felt — on a scale from I to VI.

The grade is written as a fraction of six, such as III/VI, which makes clear both the intensity and the scale being used. The lower grades are defined purely by loudness; the top two grades add a thrill — a vibration you can feel through the chest wall.

Grading is standardized precisely so that a murmur heard by one clinician can be compared against the same murmur heard by another at a later visit, without the description depending on who happened to be listening.

The Grade I–VI Scale

Grades I through IV are defined by increasing loudness with no palpable thrill. Grades V and VI both have a palpable thrill; grade VI is distinguished by being audible with the stethoscope lifted slightly off the chest.

IGrade I — Very Soft

• The faintest audible murmur, heard only after careful listening in a quiet room
• Often localized to a single spot and easy to miss at first
• May not be heard immediately on placing the stethoscope

IIGrade II — Soft

• Soft but readily heard once the stethoscope is in the right place
• Usually localized to one valve area
• Quieter than the normal heart sounds

IIIGrade III — Moderate

• Moderate intensity, easily heard over its area
• Roughly as loud as the normal heart sounds
• No palpable thrill

IVGrade IV — Loud

• Loud and often heard over a wider area of the chest
• Louder than the normal heart sounds
• Still no palpable thrill

VGrade V — Loud with a Palpable Thrill

• Loud murmur accompanied by a palpable precordial thrill (a buzzing felt through the chest wall)
• Still requires the stethoscope resting on the chest to hear
• The thrill is what separates grade V from grade IV

VIGrade VI — Palpable Thrill, Audible Off the Chest

• Loud murmur with a palpable thrill, like grade V
• Audible with the stethoscope lifted slightly off the chest wall
• The loudest end of the scale

Timing & Location Basics

Grade describes loudness, but a full description of a murmur also records when in the cardiac cycle it occurs and where it is loudest:

Timing. A murmur is classified as systolic (between the first and second heart sounds), diastolic (after the second sound), or continuous (spanning both). Timing narrows down what kind of flow abnormality is producing the sound.
Location / point of maximal intensity (PMI). The spot on the chest where the murmur is loudest, usually described relative to the valve areas (for example, the left apex over the mitral valve, or the left base). The PMI and any radiation help point toward the source.

Grade, timing, and location together form the shorthand a clinician uses to describe a murmur completely — none of the three stands in for the others.

What Grade Does (and Doesn't) Tell You

A common misconception is that a louder murmur always means worse disease. Grade reflects the intensity of the sound, not the severity of the underlying condition. A soft murmur can accompany significant disease, and a loud murmur can be relatively benign.

That's why the grade is recorded as one descriptor among several — timing, location, signalment, and the rest of the cardiovascular exam all inform the clinical picture. The grade is a measurement to document and track, not a diagnosis in itself.

Documenting a Murmur

A murmur belongs in the objective findings, written with its grade as a fraction of six, its timing, and its point of maximal intensity — for example, "III/VI systolic murmur, PMI left apex." Recording all three at each visit is what makes a change detectable: a murmur that climbs from II/VI to IV/VI over time is a finding in its own right. VetVisit AI captures the auscultation you describe in the exam room and places the graded, located finding into the note so the progression stays visible.

Frequently Asked Questions

How are heart murmurs graded in dogs and cats?

Heart murmurs are graded on a I–VI scale based on how loud they are and whether a thrill can be felt. Grade I is the softest, audible only after careful listening; grades V and VI add a palpable thrill, and grade VI can be heard with the stethoscope lifted slightly off the chest. The grade is written as a fraction of six, such as "III/VI."

What is a grade VI heart murmur?

A grade VI murmur is the loudest on the scale. Like a grade V it comes with a palpable precordial thrill — a vibration you can feel through the chest wall — but it is distinguished by being audible even when the stethoscope is held slightly off the chest surface rather than pressed against it.

What is the difference between a grade V and grade VI murmur?

Both grade V and grade VI murmurs are loud and both have a palpable thrill. The difference is that a grade V murmur still requires the stethoscope resting on the chest to hear, while a grade VI can be heard with the stethoscope lifted slightly off the chest wall.

Does a louder murmur mean more severe heart disease?

Not necessarily. The grade reflects the intensity of the murmur, not the severity of the underlying disease — a soft murmur can accompany significant disease and a loud one can be relatively benign. Grade is one descriptor recorded alongside timing, location, and the wider clinical picture, and it is not a diagnosis on its own.

How should a heart murmur be documented?

A murmur is recorded with its grade as a fraction of six (for example, "III/VI"), its timing (systolic, diastolic, or continuous), and its point of maximal intensity or valve location. Capturing these together at each visit makes it possible to see whether a murmur changes over time.

Heart Murmur Grades in Dogs and Cats (I–VI)

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