The term heart ‘murmur’ refers to a disturbed blood flow within the heart itself, which creates an extra sound or noise. It’s this sound that the vet hears when listening with a stethoscope against your pet’s chest.
The heart is designed like a one-way street. Blood is only meant to flow in one direction on its journey through the organ. If something interrupts the blood flow, like putting a large rock into a moving body of water, the turbulence creates a noise.
Heart murmurs aren’t a condition on their own, but rather a symptom of another underlying medical issue.
A heart murmur is not exclusively associated with older dogs or cats, but may start at any age. Some pets are born with a certain type of murmurs, while others develop them as they get older.
If the heart murmur is severe enough, it can be heard and even felt when you lay your hand over your pet’s heart. If you suspect your dog or cat might have a heart murmur, seek the medical advise asap.
What’s Causing those Irregular Heart Sounds
The anatomy of the heart and the precision with which all the working pieces fit together is quite amazing. For example, oxygenated blood from the lungs enters the left atrium. The atrium contracts pushing the blood into a larger chamber, the left ventricle. The latter then contracts to push blood around the body. But this means when a part becomes faulty, just like a misfiring car engine, it no longer works so effectively.
One of the commonest cause of heart murmur in dogs is valve disease. The mitral valve is like a one-way swing door, policing the path from the left atrium to the ventricle. A common problem in older dogs is myxomatous (a benign tumour of connective tissue containing mucus or gelatinous material) Thus the valve becomes stiff and thickened – a condition known as mitral valve disease. Like a door with a chunk taken out of it, the valve no longer shuts snuggly. The result being blood can flow in the wrong direction, which the vet hears as a murmur.
Heart valves are tethered to the heart muscle with special stretchy cords called ‘chordae tendineae’. Again, these can stretch and allow leakage. More serious still is if those chords rupture.
Can It Lead to a Dog Heart Attack?
This can cause a seemingly normal dog to develop acute heart failure in a form of doggy heart attack. But it isn’t just leaky valves that can cause a murmur. Thickening of the heart muscle (hypertrophic cardiomyopathy) or an enlarged heart (dilated cardiomyopathy) can also do this.
What About Heart Murmur in Cats?
A heart murmur in cats can happen, just like in any other pets. But our feline friends tend to take life easy and do less ball chasing than their canine cousins. This means cats are particularly good at hiding the early symptoms of heart disease.
This makes regular vet checks even more important for cats. A veterinarian picking up the murmur early is best placed to prevent heart disease developing.
Is there a Genetic Link?
Some dog breeds carry a higher risk of developing heart disease than others. This is because of a genetic link that is passed down from the parent to the puppies. If the puppy is born with a heart defect this is known as a congenital or ‘present at birth’ problem. Examples of this include a patent ductus arteriosus or subvalvular aortic stenosis.
However, it’s also possible for the heart to work normally at birth, but start to fail prematurely in adult life. The latter is known as acquired genetic heart disease. But life is rarely that simple and a heart murmur in dogs are no different. Not all acquired murmurs or congenital heart disease are inherited, but can develop for other reasons.
What is clear is that certain breeds, such as the Cavalier King Charles Spaniel have a vastly higher risk of developing a murmur than other breeds.
In an ideal world, breeders would only use dogs with healthy hearts to breed from. But again, life is rarely straightforward. An adult may have a normal heart and only develop the heart murmur in dogs in later life, when their breeding career is over.
Signs of a Heart Murmurs
A heart murmur in dogs can lead normal lives for years. However, there may come a point when the heart starts to struggle. At this point, the dog may show signs of heart disease. Typically, this is when the dog starts to enter congestive heart failure.
Signs of this include:
• Lack of energy
• Reluctance to walk
• Heavy breathing
• Breathing more rapidly
• A cough, especially at night or when resting
• A blue tinge to normally pink gums
• A racing heart rate
• Poor appetite
• A swollen belly (right-sided heart failure.)
If you notice any of these signs, especially if the dog has a heart murmur, see the vet immediately.
Diagnosing Heart Murmurs
The first step in diagnosing the murmur is to recognise its presence. This is done by the vet or cardiologist listening to the heart with a stethoscope.
They will listen over all of the chest areas, on both the left and right sides. This gives clues as to the exact location within the heart from which the murmur is generated. This can help with reaching a diagnosis and deciding on a course of action.
Types of Heart Murmurs
Veterinarians distinguish three different types of heart murmur based on when the sound is heard during the heart cycle:
• Systolic heart murmurs represent the majority of canine cases and take place during the systole phase as the heart muscle contracts.
• Diastolic murmurs are very rare in dogs, but they take place when the heart muscle relaxes between two heartbeats.
• Continuous murmurs (also known as to-and-fro murmurs) happen throughout a dog’s regular cardiac cycle.
An important tool vets use to monitor a dog’s heart murmur is to ‘grade’ the murmur. Grading is done on a sliding scale from 1 to 6. This is where grade I is the softest of murmurs, which is difficult to hear with a stethoscope even in a quiet room. Grade 6 is the loudest murmur possible, where the turbulent blood flow is so marked it can sometimes be heard with the naked ear.
If the murmur is grade III or above, then further tests may be necessary. Typically these include one or all of the following: an ultrasound heart scan, a chest x-ray, or an ECG. These results give the vet an accurate view of the heart’s health and what treatment, if any, is necessary.
Heart Murmur Grades
Heart murmurs also differ by loudness, which reflects the amount of disturbance present in the heart. Veterinarians grade canine heart murmurs on a scale of 1 (mild) to 6 (severe):
• Grade 1 heart murmurs are very quiet and can barely be detected with a stethoscope. This type of murmur is only heard intermittently, typically in one location on the chest.
• Grade 2 is quiet, but can be easily heard with a stethoscope.
• Grade 3 heart murmurs have intermediate volume that is consistently heard.
• Grade 4 consists of loud murmurs that can be heard on both sides of the chest.
• Grade 5 murmurs are quite loud and is easily heard with a stethoscope. It can also be felt by placing your hand against the dog’s chest.
• Grade 6 is a very loud murmur that can be heard and even felt without a problem when you place a hand on the dog’s chest. It can also heard with a stethoscope placed a few inches off of the body wall.
It should be noted that the loudness of the murmur is not always directly correlated with the severity of the disease.
Heart Murmur Configurations
The heart murmur configuration (also called quality of the murmur) describes the way the murmur sounds. There are four types of heart murmur configurations.
• Plateau murmurs have uniform loudness and are typically associated with aortic regurgitation.
• Crescendo-decrescendo heart murmurs grow louder and then softer, with common associations to pulmonic or aortic stenosis.
• Decrescendo heart murmurs start loud and then get quieter. They’re typical of diastolic murmurs and are commonly associated with a ventricular septal defect or aortic regurgitation.
• Continuous murmurs, also called machinery quality murmurs, are associated with a congenital heart defect called patent ductus arteriosus.
Treating Heart Murmurs
Not all heart murmurs require treatment. Simply keeping the dog slim and active, is often all that’s needed for grades 1 & 2.
With louder murmurs, there are medications which can support how the heart pumps and prolong a good quality of life. These drugs include angiotensin-converting enzyme inhibitors, diuretics, and positive inotropes.
When a heart murmur is identified in your healthy dog, don’t panic. There’s every chance the dog may never develop full-blown heart disease.
Your vet will record the grade of the heart murmur in dogs as well as the heart murmur in cats, along with their heart rate. They will use this to monitor your canine companion and spot signs of deterioration. Should this happen, then further tests may be necessary.
Happily, modern medications can support a dog with heart disease and enable them to continue with the excellent quality of life for months or years to come.
Remember, each dog is an individual. Some defy the odds and outlive their predicted lifespan, whilst others can sadly suffer a catastrophic event, such as a heart attack, and deteriorate suddenly. But by being proactive and working with your vet, there’s every chance that you can make a difference and keep your pet happy for longer.