The Only Locally-Owned Emergency and Specialty Hospital in Minnesota

Pet Heart Murmurs

What is a heart murmur?
A heart murmur is an abnormal sound that a veterinarian may discover when listening to your pet’s heartbeat with a stethoscope. This sound is a result of a disturbed blood flow within the heart, the aorta, or the pulmonary artery.

What does a “soft” or “loud” heart murmur mean?
If your veterinarian hears a murmur, he/she will grade it according to this scale from I to VI based on the murmur’s audibility:
Grade I: barely audible
Grade II: soft
Grade III: intermediate loudness
Grade IV: loud murmur that radiates widely
Grade V: very loud
Grade VI: extremely loud

What does it mean that my puppy was diagnosed with an “innocent murmur”? 
If your pet is a young puppy or kitten with a Grade I or II murmur, it is most likely an “innocent murmur”. These types of murmurs appear when your pet is 6-8 weeks old and usually by the time your pet is 4-6 months old, he/she will outgrow the murmur. This is very common in large breed puppies as they are growing.

What are signs to look out for if a murmur becomes a more serious issue?
Murmurs can be benign or they can be early signs of congestive heart failure.  If your pet has a heart murmur, these are the early warning signs of heart disease to watch for:

  • Coughing
  • Changes in breathing–labored or rapid breathing
  • Changes in sleep posture
  • Shortness of breath
  • Lack of energy/tires easily/lethargy
  • Exercise intolerance
  • Fainting
  • Restlessness, especially at night
  • Changes in appetite
  • Sensitivity to heat or cold

What are the causes of CHF?
Common causes of CHF include: old age, injury, infection, unbalanced diet, lack of exercise. Other pets may be born with heart defects.

What can I do to keep an eye on my pet’s heart murmur at home? 
Ask your veterinarian to teach you how to track your pet’s resting respiratory rate (RRR) at home. This way, if your pet’s condition changes, you can notify the veterinarian right away. A change in breathing rate could be the earliest sign of congestive heart failure.

  • Have your veterinarian establish a baseline.
  • Monitor weekly once pet has cardiac enlargement.
  • Rate should be less than 30 breaths per minute.
  • Keep a diary or use the RRR app (available at or on the app stores for iPhone® or Android™ Smartphones)
  • Have your veterinarian provide you with your RRR (usually less than 30 breaths/minute) or a percentage increase from baseline (usually >20% for 6+ hours), so they know when to bring in their dog for a heart examination.

Now what?
Your veterinarian will be able to diagnosis your pet after looking into his/her medical history, performing a physical examination, listening to your pet’s heart and lungs, taking x-rays, and running additional tests. Once your veterinarian is able to diagnose your pet, a treatment plan can begin. Talk to your veterinarian today if you are concerned about your pet. If your veterinarian does not offer advanced cardiology services, ask about a referral to the Animal Emergency & Referral Center of Minnesota’s board-certified cardiologist, Dr. Michelle Rose.

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