Meaning of Heart Murmur Grades 1–6

HeartQ&AMeongsiljang Veterinary Advisory Board

Heart murmur grades are a classification system that categorizes the intensity of the murmur heard during auscultation on a scale of 1 to 6. We’ve outlined the meaning of each grade, its level of urgency, and guidelines for when to visit the vet.

What Are Heart Murmur Grades 1–6?

A veterinarian listens to a puppy’s chest with a stethoscope to assess the grade of a heart murmur.

The heart murmur grading system is a standardized classification that rates the intensity of heart murmurs heard through a stethoscope on a scale from grade 1 to grade 6. It’s important to understand that a higher grade simply means a louder sound; it does not necessarily correlate directly with the severity of the underlying condition. From grade 5 onward, the murmur is so intense that a palpable thrill (vibration) can be felt by placing a hand on the chest, whereas a grade 4 murmur is loud but lacks this accompanying vibration. Even for grades 1 and 2, an accurate assessment requires a comprehensive evaluation that considers the patient’s age, breed, and clinical symptoms.

Why Are Heart Murmurs Graded?

A heart murmur is a sound caused by abnormal blood flow within the heart. Because the underlying causes can vary widely—including valvular abnormalities, ventricular septal defects, and early-stage heart failure—veterinarians grade murmurs on a scale of 1 to 6 based on their intensity (loudness). The location where the sound is most audible (the point of maximum intensity) and the timing of its occurrence (systolic or diastolic) are recorded as separate characteristics of the murmur, independent of the grade. The grade itself does not directly determine the treatment plan; rather, it serves as a starting point for deciding whether additional diagnostics—such as echocardiography, radiographs, or blood pressure monitoring—are needed. A grade 3 murmur, for example, carries different implications for a 10-year-old small-breed dog than for a 1-year-old large-breed dog.

Heart Murmur Grades 1–6 at a Glance

Item	Sound loudness	Presence of thrill
Grade 1	Barely audible only after concentrating for several minutes in a quiet room	None
Grade 2	Faint sound heard within a few seconds of auscultation	None
Grade 3	Clearly audible at moderate intensity	None
Grade 4	Loud, but no chest vibration	None
Grade 5	Loud and a chest vibration (thrill) is felt	Present
Grade 6	So loud it can be heard even with the stethoscope lifted off	Present

Based on the modified Levine grading system (Textbook of Cardiovascular Medicine in Dogs and Cats)

What Does Each Grade Mean?

According to veterinary internal medicine textbooks, the key points of concern vary by grade.

Grades 1–2: These murmurs may be heard temporarily even in healthy young puppies (physiologic murmurs). If there are no symptoms, regular follow-up monitoring is the standard approach.

Grade 3: This is a clearly audible murmur of moderate intensity, which may be localized to a specific area or radiate to other parts of the chest. An echocardiogram is recommended to assess for possible valvular disease or congenital heart defects.

Grades 4–6: These are high-intensity murmurs. Grade 4 murmurs are loud without a palpable thrill, while grades 5 and above are accompanied by a palpable chest thrill. These often lead to further diagnostic testing to evaluate for advanced valvular disease or congenital heart defects.

An anatomical illustration showing the auscultation sites for a dog’s heart and the meaning of each heart murmur grade

When to Seek Immediate Veterinary Care

The symptoms that appear alongside the stage number are more telling of danger. If your pet exhibits any of the following, don’t delay—seek veterinary care right away. - Has fainted or suddenly collapsed - Breathing faster or with more effort than usual, even at rest - Gums appear pale or bluish-purple - Unable to catch their breath for a long time after exercise - In dogs: Repeated coughing at night (coughing is not a typical symptom of heart disease in cats)

What Pet Owners Should Do After Learning the Grade

If a heart murmur is detected, your veterinarian will guide you on whether further testing is needed, along with the murmur’s grade. An echocardiogram is generally recommended if the murmur is grade 3 or higher, if specific auscultatory findings are present, or if clinical symptoms are observed. Before the appointment, it’s very helpful to consistently record your pet’s resting respiratory rate at home (count the number of chest rises and falls in 30 seconds, then multiply by 2). Please contact your clinic promptly if you notice a noticeable increase in the resting respiratory rate compared to normal, or if your pet appears to be having difficulty breathing over consecutive days.

A guardian gently places a hand on a sleeping puppy’s chest to measure its resting respiratory rate.

Breed- and Age-Specific Points of Concern

Small-breed dogs (10 years and older): Myxomatous mitral valve degeneration is common. Regular echocardiography is recommended if the condition is stage 3 or higher, or if specific auscultatory findings or clinical symptoms are present. Even with a lower grade, consult your veterinarian if you notice any changes in symptoms. Large-breed dogs (young age): Dilated cardiomyopathy or congenital heart defects may be present. Detailed testing is necessary if symptoms appear, even if the initial grade is low. Cats: Hypertrophic cardiomyopathy is often missed by auscultation alone. Consider an echocardiogram if there are episodes of fainting or breathing difficulties, even if no heart murmur is detected. Puppies: Physiological murmurs of grade 1–2 may disappear as the puppy grows.

Common Misconceptions Among Pet Owners

The simplistic equation that "lower grade equals safe, higher grade equals end-stage" is not accurate. The noise grade does not necessarily correlate with the severity of the underlying disease, and the clinical significance can vary greatly depending on the animal's age, breed, and accompanying symptoms, even within the same grade. The grade is just one clue; the final diagnosis is made by comprehensively evaluating ultrasound, X-rays, blood pressure, and symptoms.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

If my pet has a grade 1 heart murmur, does it need treatment?

In most cases, we simply monitor the condition. However, it is essential to have regular check-ups at the intervals recommended by your veterinarian, and if any symptoms arise, a thorough diagnostic examination is immediately necessary.

Does a lower heart murmur grade mean the condition has improved?

Not necessarily. The intensity of heart murmurs can vary depending on a variety of factors, so it’s difficult to determine improvement based solely on changes in murmur grade. An ultrasound is needed to directly assess the heart’s structure and function.

Can I use a stethoscope to check my pet myself?

While it’s possible to compare the volume of sounds, assigning a specific grade is difficult. Instead, consistently recording your pet’s resting respiratory rate at home can be very helpful.

Do cats use the same 1-6 rating system?

Yes, we use the same modified Levine grading scale. However, since feline cardiomyopathy often progresses without producing a heart murmur, careful observation of clinical signs is even more important.

If a heart murmur is present, is anesthesia or surgery contraindicated?

It depends on the grade and the heart condition. After assessing safety with a preoperative cardiac ultrasound, the veterinarian can adjust the anesthesia protocol accordingly.