Heart murmurs in dogs are any abnormal sound made by the heart and they can range from being very minor and natural occurrences to more serious problems that can sometimes be fatal. A murmur will be present any time there is an abnormal blood flow to the heart, usually because of turbulence in the blood flow.
The Grades of Heart Murmurs in Dogs
Heart murmurs can either be very minor or they can be very serious. In order to efficiently indicate which kind dogs have, veterinarians use a scale of I-IV in order to indicate their severity.
- Grade I heart murmurs are very quiet, heard at random intervals, and heard usually only in one specific area of the chest.
- Grade II heart murmurs are a bit louder than a Grade I murmur, have regular patterns, and can only be heard in one specific area of the chest.
- Grade III heart murmurs are louder still than Grade II murmurs, have regular patterns, and can be heard in different areas of the chest.
- Grade IV heart murmurs are the loudest murmurs and can be both heard through a stethoscope, as well as felt when a hand is placed over the chest. In fact, these murmurs can be felt anywhere the pulse can be felt on the body.
Causes of Heart Murmurs in Dogs
There are 4 main causes of heart murmurs:
- Innocent or physiologic;
- Disease (pathologic);
- A Structural problem with the heart;
- A Condition unrelated to heart disease (extracardiac).
Physiologic heart murmurs, sometimes called innocent heart murmurs, are common heart murmurs that will not affect your dog’s health in any way. They are almost always given a category of Grade I or Grade II. These heart murmurs will often be heard in young pups that are 6-8 weeks old, especially in those that are of a large breed. These types of murmurs are benign and although a vet will want to keep record of it, they will disappear by the time the puppy is 4-5 months old.
A structural problem with the heart indicates an actual physical problem in the heart that has occurred because of trauma to the heart or because the dog was born with the heart defect.
When this is the reason for the heart murmur, the blood flow is being disturbed with due to a defect such as a leaky heart valve, a change in a valve or large blood vessel whether it’s a constricting or thickening, or a hole between the chambers of the heart. When the murmur can be attributed to this type of damage, one of the most common causes is a condition called “mitral insufficiency,” which is when the mitral valve in the heart has thickened and begins to leak. This is a condition that is especially common among smaller breeds. In older dogs, bacterial endocarditis is a condition that’s a common cause of heart murmurs.
Extracardiac heart murmurs are also known as “functional heart murmurs” because they don’t affect the dog’s life all that greatly. They are always due to a condition that has nothing to do with the heart, but is still causing it to produce a murmur. This happens most often when that underlying condition has caused the blood to become too watery and runny, causing it to flow through the heart too quickly and cause the murmur.
The underlying condition causing it can range from fever or infection, pregnancy, weight problems, anemia and/or hypoproteinemia. When puppies are young, anemia and/or hypoproteinemia is commonly seen with certain parasites, worms, fleas and ticks, and can typically be treated very easily. When adult dogs have extracardiac heart murmurs, it’s typically due to the dog becoming anemic due to a major loss of blood, or due to a much more serious underlying disorder.
Diagnosing and Treating a Heart Murmur
Diagnosing a heart murmur is very easy. Your vet will easily be able to hear if one is present when they examine your dog, especially your dog’s chest area, with a stethoscope. And, it will even be easy for your vet to be able to tell you whether or not the heart murmur is something that you should be concerned about.
If the dog is still very young and the murmur has a very low intensity, the vet will definitely mention it to you, as well as the fact that it’s nothing to be worried about. They will write it down in your dog’s medical chart and will also likely ask you to come back in a few weeks simply to track the murmur and check for any changes in its location or intensity. This is just so your vet can have a record of it and while it sounds worrisome, really is just probably a common and innocent heart murmur.
If the dog is very upset or excited, this could also cause a heart murmur so if there’s a request for a follow-up, try to make sure your dog is a bit calmer on his next visit. That can be difficult, but you’re more likely to find that the murmur has disappeared. Innocent murmurs such as these don’t usually require any treatment at all.
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If the heart murmur is more severe, indicating possible structural heart disease or an extracardiac issue, your dog will most likely be exhibiting other symptoms that are much more severe. These can include:
- Loss of appetite
- Weight loss
- Difficulty breathing, especially in the middle of the night or after the dog has been lying down for long periods of time
- Weakens and tires easily
- Has collapsing or fainting spells
- A pale color in the gums
- Excessive coughing
- An irregular heart rate that can be felt and/or heard
When a heart murmur is due to a structural problem in the heart or extracardiac problems, further diagnostic testing will need to be done. This might include ultrasounds, x-rays, electrocardiograms, and echocardiograms. If structural damage is suspected, a Doppler exam will most likely be given. This ultrasound is an advanced type of echocardiogram that can physically show the heart, its movements, and the rate of blood flow so that problems in specific valves can be pinpointed to find the problem easier and with more accuracy.
The ongoing treatment of heart murmurs due to structural damage or extracardiac reasons is either through a specialized diet, medications, supportive care, or a combination of all three. If the heart murmur is due to congenital heart defects, such as pulmonic stenosis or patent ductus arteriosus, surgery might be an option that will correct both the murmur and the underlying cause.
Outlook for Dogs With Heart Murmurs
Giving a general prognosis for dogs with heart murmurs can be difficult because they so greatly vary between types and severity. However, there are some general guidelines that your vet will likely give you so you can be prepared as to what to expect.
- Innocent or physiological heart murmurs are not at all serious and are considered so insignificant that they don’t even typically require treatment. The prognosis for any dog that has one of these murmurs is excellent and they will likely go on to life a long and happy life.
- When heart murmurs are due to congenital heart disease the prognosis still greatly varies because each scenario will be different. If the disease can be dealt with through surgery, the prognosis is generally very good.
- Heart murmurs that develop due to mitral insufficiency have a very good prognosis as well, although the dog will need to take medication for the rest of their life.
- The conditions that cause heart murmurs with the gravest prognosis are bacterial endocarditis and dilated cardiomyopathy.
Heart murmurs in dogs can be a very scary thing, and it can be natural to panic after your dog has been diagnosed with one. However, keep in mind that most heart murmurs are very innocent and there’s nothing at all to be concerned about. Make sure your dog has regular checkups at the vet so you can both be alerted to the first sign of one, and start to record or treat it as necessary. Just like anything else, heart murmurs and their underlying conditions are generally much easier to treat when they’re caught right away.