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Heart Murmur in Dogs: What You Need To Know

Dog with heart murmur cuddles in owners lap

Heart murmurs in dogs can be anxiety-induced, but they’re also one of the most commonly diagnosed health conditions in the canine world. You probably have many questions if your dog was recently diagnosed with a heart murmur. 

You’re likely also feeling scared for your precious pet, which is completely understandable because we love our pets, too! Gaining a better understanding of what a heart murmur is can ease some of that fear and help you know how to help your dog, keeping them healthy and healthy for as long as possible.

What Is a Heart Murmur?

Your dog’s heart beats like yours — blood flows into and then is pumped back out of the heart’s four chambers (known as atria and ventricles). This flow of blood through the heart creates your dog’s heartbeat. 

When your veterinarian checks your dog’s heart, they listen for two distinct sounds — the “lub dub.” These sounds are made when the heart valves open and close, which they do in a very specific order to keep the blood pumping smoothly throughout the body.

As blood returns from the body, it enters the right atrium, travels into the right ventricle, and heads into the lungs through the pulmonary valve. After it has been oxygenated, it travels back into the heart, heads through the left ventricle, and then back out to provide the body with newly re-oxygenated blood once again. 

The “lub” is the noise of the mitral and tricuspid valves closing, stopping the blood from flowing backward. The “dub” is the other two valves, the aortic and pulmonary valves, doing the same. 

A heart murmur is an extra sound within that cycle, although most are found between the “lub” and “dub.” Some heart murmurs are quiet and can be easily missed, while others are so loud they can even drown out the normal sounds of the heart beating. 

However, all heart murmurs signify that some amount of turbulent blood flow is occurring. Heart murmurs in dogs are often described as a “whooshing” noise.

What Can Cause a Heart Murmur?

Physiologically, there are four main reasons the flow of blood would travel through the heart abnormally. Any of the heart valves could have a size or shape abnormality, there may be an obstruction somewhere in the heart, the valve may not shut as tightly as it should, or there may be an abnormal opening between heart structures. 

Determining the cause of a heart murmur in dogs is challenging because those four instances can occur for many different reasons. For example, many heart murmurs in dogs (especially those diagnosed in puppies) are genetic. 

Certain dog breeds are more likely to develop these congenital heart murmurs, with boxers, Doberman Pinschers, miniature and toy poodles, and King Charles Cavaliers being some of the most frequently diagnosed. 

Larger breed dogs are most likely to develop a cardiac disease called dilated cardiomyopathy (DCM), which causes the mitral valve to leak. While this can be a congenital issue, it’s also described as pathologic. 

Pathologic causes can be due to structural issues inside the heart (like heart disease or DCM) or extracardiac problems (like anemia, pregnancy, or obesity). 

Heartworm is also an extracardiac problem. With heartworm, a parasite is passed through a mosquito bite, causing extensive damage to your dog’s heart. This damage can also predispose your dog to develop a heart murmur. Luckily, heartworm is also something that can be easily prevented by giving your dog a monthly preventative

What Are the Symptoms of a Heart Murmur?

Most heart murmurs are asymptomatic and are only diagnosed during your dog’s routine annual exam. These murmurs are usually completely benign, very rarely causing problems. 

Many puppies will even grow out of them before they’ve ever been diagnosed. However, if the heart murmur is significant, you may notice other symptoms, especially as your dog grows. 

If you notice any of the following signs, you should seek a veterinary assessment immediately. 

  • Breathing issues (frequently occurring without physical activity or in the middle of the night)
  • Coughing
  • Exercise intolerance
  • Fainting spells
  • Pale gums
  • Poor appetite
  • Stunted growth (in puppies)
  • Weight loss

How Serious Is a Heart Murmur?

Heart murmurs in dogs are graded from I to VI, with I being the mildest and VI being the most severe. How loud the heart murmur is directly related to how much turbulence is happening inside the heart, but it’s not the only factor in grading a murmur’s severity.  

  • Grade I – These murmurs are incredibly soft, and some may not even be able to be picked up by a stethoscope, even in a quiet room.
  • Grade II – If a heart murmur is designated as a grade II, it is still soft but is easier to be auscultated by your veterinarian.
  • Grade III – This type of murmur is even louder but can only be heard on one side of your dog’s chest. Grade III murmurs are where they begin to get more serious and have the potential to cause problems.
  • Grade IV – When a heart murmur is grade IV, it is not only loud but can now be heard on either side of the chest wall.
  • Grade V – At grade V, it may be possible to feel the murmur by placing a hand on the dog’s chest.
  • Grade VI – This is the most severe type of heart murmur, which can be both loudly heard and felt. 

What Are the Types of Heart Murmurs?

There are three basic types of heart murmurs in dogs — systolic, diastolic, and continuous — which are named for where in the heart cycle they occur. They may also be categorized as either “short” or “long.” 

  • Systolic – This type of heart murmur happens when the heart muscle is contracting. Systolic murmurs are the most common type and are caused by heart issues like pulmonic stenosis, subaortic stenosis, or endocarditis.
  • Diastolic – If the heart murmur occurs when the heart is relaxed, it’s known as a diastolic murmur. However, diastolic heart murmurs in dogs are a lot less common. Aortic insufficiency is one of the main triggers of this type of murmur.
  • Continuous – Heart murmurs in dogs that can be heard during both the systolic and diastolic parts of the heartbeat cycle are known as continuous. A common condition in puppies, known as patent ductus arteriosus (PDA), causes a continuous heart murmur, as does a ventricular septal defect. 

How Can You Help Your Dog?

If you suspect your dog may have a heart murmur, your first stop should be your veterinarian’s office. They’ll be able to listen to their heart or even order additional diagnostic testing. A diagnosis and potential course of treatment are usually decided after putting multiple puzzle pieces together.

  • Blood work – Blood work can help rule out underlying causes of heart murmurs, like heartworm and anemia.
  • Echocardiogram – A specialized ultrasound of the heart that checks its function and structure. Echos can also help narrow down the exact location of a heart murmur.
  • Electrocardiogram – Also known as an ECG or EKG, this painless test records the heart’s electrical signal. Small stickers are attached to your dog, followed by electrodes that will follow the signal as it travels through the heart. ECGs are specifically beneficial for diagnosing arrhythmias.
  • X-ray – Some vets may want to take a chest x-ray, which won’t specifically diagnose the heart murmur but can indicate whether your dog’s heart is enlarged or other structural defects may be contributing. 

However, a heart murmur on its own isn’t necessarily treated. Many are simply monitored, requiring regular check-ups to ensure that it hasn’t progressed or changed. Instead, veterinarians focus on treating the underlying cause of the murmur and managing any related symptoms. 

In rare occasions, more significant heart murmurs (like patent ductus arteriosus and pulmonic stenosis) may require surgical corrections. These will be done by a veterinary cardiologist in a specialty hospital. 

But what can you do at home, in between all the vet visits? One management technique is minimizing their stress level, especially if their heart murmur is a grade III or above. 

When your dog is anxious, their heart naturally beats much faster than it usually does. The harder and faster their heart pumps, the more at risk they may be for complications related to their murmur or the underlying condition that may be triggering it.