What are the different grades of heart murmurs and their clinical significance?

Heart Murmur Grading System

Heart murmurs are graded on a 6-point intensity scale (grades 1 through 6) for systolic murmurs, with grade 3 or louder typically indicating organic heart disease requiring echocardiographic evaluation. 1, 2

The 6-Point Grading Scale

The traditional grading system assesses murmur intensity as follows:

• Grade 1/6: Very faint murmur, barely audible even with optimal listening conditions 2
• Grade 2/6: Soft murmur but readily heard with stethoscope 1
• Grade 3/6: Moderately loud murmur without palpable thrill 2
• Grade 4/6: Loud murmur with palpable thrill 1
• Grade 5/6: Very loud murmur, audible with stethoscope partially off chest 1
• Grade 6/6: Extremely loud murmur, audible with stethoscope entirely off chest 1

Diastolic murmurs are graded on a 4-point scale (grades 1 through 4), though this distinction is less clinically relevant since all diastolic murmurs require immediate evaluation regardless of intensity. 2

Clinical Significance by Grade

Grade 1-2 Systolic Murmurs

In asymptomatic adults with grade 1-2/6 midsystolic murmurs at the left sternal border and no other abnormal cardiac findings, the murmur is typically innocent and requires no further workup. 2

These low-grade murmurs are often functional, related to:

• High cardiac output states (pregnancy, fever, anemia, thyrotoxicosis) 1
• Flow into dilated vessels 1
• Thin chest wall transmission 1

However, grade 1-2 murmurs require echocardiography when accompanied by: 2

• Symptoms (syncope, angina, heart failure, thromboembolism)
• Signs of infective endocarditis
• Abnormal physical findings (widely split S2, systolic ejection sounds)
• ECG or chest X-ray abnormalities (ventricular hypertrophy, atrial enlargement)

Grade 3 or Louder Systolic Murmurs

All grade 3 or louder systolic murmurs warrant echocardiographic evaluation, as they correlate strongly with organic heart disease. 2, 3

The landmark Freeman and Levine study from 1933 established that all patients with grade 3 or 4 murmurs had either organic heart disease or anemia, making louder systolic murmurs a significant finding requiring investigation. 3

The intensity of regurgitant murmurs correlates well with severity: 4

• For aortic regurgitation: grade ≥3 predicts severe regurgitation in 71% of cases
• For mitral regurgitation: grade ≥4 predicts severe regurgitation in 91% of cases

All Diastolic Murmurs

Diastolic murmurs of any grade virtually always represent pathological conditions and require immediate echocardiographic evaluation. 1, 2, 5

This is a critical clinical pearl—unlike systolic murmurs where grade matters significantly, diastolic murmurs are pathologic regardless of intensity. 2

Holosystolic and Late Systolic Murmurs

All holosystolic (pansystolic) or late systolic murmurs at the apex or left sternal edge require echocardiography regardless of grade. 2

These murmurs indicate:

• Mitral regurgitation (holosystolic at apex radiating to axilla) 6, 5
• Tricuspid regurgitation (holosystolic at lower left sternal border) 6, 5
• Ventricular septal defect (holosystolic at left sternal border) 6, 5

Assessment Beyond Grade

Murmur grading must be integrated with other auscultatory characteristics: 1, 2

• Timing: Systolic, diastolic, or continuous
• Configuration: Crescendo, decrescendo, crescendo-decrescendo (diamond-shaped), or plateau
• Location and radiation: Where maximal intensity occurs and where it travels
• Pitch: High, medium, or low frequency
• Duration: How long the murmur lasts in the cardiac cycle

Dynamic Auscultation Findings Requiring Workup

Certain maneuver responses indicate pathology regardless of baseline grade: 2

• Increases with Valsalva or standing, decreases with squatting: Suggests hypertrophic cardiomyopathy or mitral valve prolapse
• Increases with handgrip or transient arterial occlusion: Requires further evaluation
• No increase after premature ventricular contraction or long R-R interval in atrial fibrillation: Suggests mitral regurgitation or ventricular septal defect rather than aortic stenosis

Critical Pitfalls to Avoid

Do not assume all soft murmurs are innocent—context matters. 2

Grade 1-2 murmurs require workup when:

• Patient is symptomatic
• Other abnormal cardiac findings present
• Murmur is diastolic, holosystolic, or late systolic in timing

Do not rely solely on murmur grade to assess severity of regurgitation in ischemic or functional mitral regurgitation. 4

The correlation between intensity and severity is weaker (r = 0.47) in ischemic/functional mitral regurgitation compared to organic valve disease (r = 0.64). 4

In elderly patients with systemic hypertension, grade 1-2 midsystolic murmurs may relate to sclerotic aortic valve leaflets or flow into tortuous vessels rather than true innocent murmurs. 2

Echocardiography may detect trivial or physiological valvular regurgitation in many normal patients who have no audible murmur at all, so the absence of a murmur does not exclude valve disease. 2