Information about Heart Murmurs and Disease

Information about Heart Murmurs and Disease
By Emily Hoppmann, DVM

About the Diagnosis of a Heart Murmur:

A heart murmur in most dogs is due to a leaky mitral valve within the heart and is usually a problem affecting the hearts of adult dogs. In animals, just like in humans, the mitral valve is a trapdoor type of structure that separates the two chambers of the left side of the heart. The tricuspid valve separates the chambers of the right side of the heart, but is usually the second valve to have an issue and not the primary cause of disease. Both of these one-way valves ensure that the heart functions efficiently by preventing backflow of blood each time the heart contracts – it makes sure that the blood is only allowed to flow in the correct direction, and the sound of a murmur is the sound of blood going the wrong direction. In a normal dog with a properly-functioning mitral and tricuspid valves there is no murmur heard because the blood that enters the heart moves through correctly and into circulation thanks to these valves, or doors, within the heart.

A heart valve disorder has many names: “endocardiosis”, “degenerative valvular disease”, and “myxomatous valve degeneration” are some of the more common synonyms. The different names refer to the same process: an abnormal thickening and distortion of the heart valves that occurs in some adult or older dogs. It can be thought of as a form of premature aging of the heart valve tissue. Endocarditis can also cause heart disease and that is when the actual valves of the heart become infected by bacteria. This is usually a direct result of bacteria landing on the heart valve due to bacteria in the blood stream, most commonly because of dental disease. This is why dental health is so important and we recommend dental cleanings and having your dog on a pulse therapy antibiotic to decrease the number of bacteria in the mouth. The main goal when we encounter heart disease, regardless of the cause, is to not allow the heart disease to progress to the fatal condition of congestive heart failure or to slow the progression of disease as much as possible.

Small breeds are most commonly affected by this condition, although it can sometimes occur in any size dog, including large and giant breeds. In about two-thirds of the cases, the mitral valve alone is affected and since it is on the left side of the heart the clinical signs are a result of the fluid backing up into the lungs; in about one-third, both the mitral and tricuspid valves are affected; and rarely is the tricuspid valve alone involved (how many valves are diseased usually depends on when the heart disease is caught since it is a snowball effect once one valve is affected). Affected valves fail to seal well when they close, allowing a small amount of blood to seep back into the heart chamber where it just came from, rather than moving forward into circulation (creating a murmur). This inefficiency has two drawbacks: it compromises the amount of blood moving forward into the body’s circulation to nourish the organs, and it increases the pressure inside a part of the heart called the atrium (the chamber which receives blood that seeped back, or “regurgitated”, through the defective heart valve). Overall, a poorly functioning heart valve means that the heart has to work harder than normal to keep up the normal circulation. Since the heart is a muscle, as the leakage becomes worse over time and the heart has to work harder, resulting in the heart walls further thickening and causing more heart disease over a period of months to years, which affects the overall health of your pet. Over time, the heart starts to not be able to keep up, and symptoms such as shortness of breath, exercise intolerance (loss of stamina), and coughing, may start to become apparent. In order to avoid clinical signs and the progression to congestive heart failure, treatment involving lifestyle changes and medications are needed immediately once the heart disease is diagnosed. Medications for heart disease work very well and can restore a good quality of life, but without treatment, the heart disease may quickly become life-threatening.

In the early stages of heart disease, the only symptom may be the presence of a heart murmur. This is why it is so important to have at least bi-annual exams so that the murmur can be detected as soon as possible. The turbulence created by blood leaking through the diseased valve creates the sound heard as a murmur, which is a coarse, hissing sound heard with every heartbeat (heard when I listen to the heart with my stethoscope) as opposed to the normal thumping sound of a healthy heart. This is often the only sign that heart disease is present, and it can remains the only sign for months or years because the heart and body adapt so well. It is common for a heart murmur to be a surprising or unexpected find because heart valve disease is well-tolerated in its early and intermediate stages so your pet won’t appear to be sick at all. However, heart valve disease tends to very gradually get worse until it becomes a life-threatening condition. Over time, an increasing amount of blood is sent in the wrong direction with each heartbeat rather than moving forward in the circulation to allow oxygen to reach the organs in the body. If this process occurs to the point that the body’s ability to adapt is exceeded, then the circulation becomes disrupted, causing fluid retention within the lungs (if it is the mitral valve primarily affected), leading to labored breathing, coughing, and intolerance of exercise.

The most important thing you can do as an owner when your pet has a heart murmur or heart disease is to monitor changes in the resting breathing rate. Each day, while your pet is at rest (best when asleep) count the number of breaths taken over a minute and record this number so that if there is a change, you can let us know right away. There is also a free “app” for smart phones (both for I-phone and Android systems) that allows you to enter this information, have it emailed to us (at, set reminders for you to take a daily measure, etc. You can visit for more information on this wonderful tool. You can also simply write down the date and respiratory rate and bring it with you to your appointment if/when a change is noted. Congestive heart failure is a somewhat misleading term because it does not mean that the heart has “failed” in the sense of stopping, but it means the heart is failing to meet the body’s circulatory requirements. This results in fluid pooling in the lungs and eventually in the abdomen as well – that is why monitoring the number of breaths per minute is so important. It is a small change that gives a huge amount of information that can allow us to change foods, add medications, change current medication doses, etc. to continue to prevent the progression of the heart disease.

Some guidelines for the general care of dogs that heart valve disease include:
• Keeping our pets moving, but avoiding or reducing intense physical exercise, because the heart is under the greatest strain when it is forced to beat quickly
• Preferring lower-intensity, on-leash walks for physical activity, as long as the dog does not show signs of exhaustion or difficulty keeping up that might indicate too much activity
• Avoiding treats or foods that are rich in salt, which causes fluid retention and favors the development of congestive heart failure
• Beginning a weight-loss diet if your dog is overweight, as at least 60% of pet dogs in North America are. An excess of body weight means unnecessary extra work for the heart. We are happy to get you started on a weight-loss plan individualized for your pet

Despite these precautions, worsening heart valve function with time can lead to congestive heart failure. When it occurs, congestive heart failure may cause a dog to have trouble breathing, and the gums may take on a bluish or grey color due to lack of oxygen. The belly may become distended with fluid, and the dog often will be very inactive. Episodes of fainting can even occur. These are very advanced symptoms, and a dog should be brought to us when any changes are noted, including labored breathing, coughing, or loss of stamina so that we can try to avoid these more serious clinical signs. Fortunately, thanks to the wonderful advances in heart medications and heart specific diets many dogs with heart valve disease never develop congestive heart failure and have just a heart murmur, and no other symptoms, for their natural, normal life.
As mentioned above, heart valve disease is usually first diagnosed by the detection of a heart murmur during a routine health examination. At this asymptomatic stage when only a heart murmur is present, chest x-rays (radiographs), an ultrasound of the heart, and blood work are recommended to confirm the diagnosis and evaluate the extent of the problem and the dog’s overall health. Repeating these tests periodically will allow us to assess how rapidly the problem is advancing, if at all. An electrocardiogram may be used to check for irregular heartbeats, which may develop in the later stages of the disease.

Living with the Diagnosis:

Unfortunately heart valve disease is a process that gets progressively worse if left untreated and can take years off of an animal’s life. The good news is, again thanks to such good medication, monitoring, and lifestyle changes, it can be years after the detection of a heart murmur before congestive heart failure occurs. If your dog with heart valve disease shows any symptoms of not feeling well, it is best to have an exam done as soon as possible so that we can use these tools to help the disease from getting any worse and ensure your pet has a good quality of life.

The long-term outlook for dogs with heart valve disease but no clinical signs is good since some dogs tolerate the heart valve disease unknowingly for the rest of their lives, but others will develop congestive heart failure after simply a short-period. What we want to avoid is a dog that is showing outward signs – such as coughing, increased respiratory rate or effort, exercise intolerance. At that point, the heart disease is affecting the quality of the dog’s life negatively, and that is not something we want. This is why it is so important to catch the disease early and to start treatment right away. Dogs with heart disease generally require multiple medication daily and more frequent checkups with us. The lifespan after the onset of congestive heart failure is extremely variable and depends on the severity of the valve problem, and the dog’s response to medication. Dogs may live from days to years after developing congestive heart failure – it is very individualized and that is why our treatment plan for each patient is also specific to each individual patient.

Management of congestive heart failure includes the use of medications, low-salt diets, and exercise restriction. One medication used is a diuretic to evacuate retained fluid. Fluid accumulation in the lungs is one of the factors that cause labored breathing and cough associated with heart disease; fluid accumulation in the abdomen is one of the reasons for the belly appearing so distended. Other medications are used to help to reduce the workload of the heart so it prevents it from developing thicker and thicker walls, making the heart disease worse. As your pet’s heart disease worsens, other medications may be added to treat specific problems, doses may need to be adjusted, and we will tackle each issue together! The goal of treatment is to find a combination that keeps your dog comfortable and enjoying a good quality life.

• Give all medications exactly as directed
• If clinical signs of heart disease develop, restrict your pet’s exercise to leash walks
• If your pet is overweight, start a weight reduction program
• Do not feed salty treats
• Do not overdo physical activity with your dog. Heart valve disease is not a type of heart disease that exercise will improve. Leash walks and mild to moderate degrees of activity, as tolerated by your dog, are ideal.
• Do not be alarmed if you notice your dog’s heartbeat seems irregular when your dog otherwise seems to feel fine. Healthy dogs often have an irregular-sounding rhythm that is simply a normal variation related to their breathing. Advanced stages of mitral valve disease can cause truly irregular, chaotic heartbeat rhythms, however, and screening for this is part of what I do when listening to the heartbeat with a stethoscope. If any uncertainty exists, I can recommend an EKG to determine whether there is reason for concern.

When to Call Elgin Veterinary Hospital:
• If your dog shows lack of appetite, lethargy/sluggishness, vomiting, or diarrhea
• If your dog’s symptoms become worse or reappear, an adjustment in medication dosage may be needed so you should schedule an appointment as soon as possible

Signs to Watch For:
• Take a daily record of your pet’s sleeping respiratory rate by counting the number of breaths they take in one minute
• Monitor for coughing or difficulty breathing
• Restlessness, inability to get comfortable, especially if accompanied by labored breathing – often this is worse at night
• Exercise intolerance, especially stopping mid-walk, out of breath, when the same amount of exercise used to be manageable without any difficulty

Signs In advanced disease:
o Bluish or grey gums
o Swollen belly
o Fainting spells or severe weakness
o Trouble using the rear legs
o Abdominal breathing

Routine Follow-Up Care:
The frequency of follow-up examinations depends upon the severity of your dog’s condition. Dogs just started on medications (or new medications, dose changes, etc.) should be rechecked in 4 weeks. Dogs with no symptoms or mild symptoms should be evaluated every 4 months. More severely affected dogs should be examined every 2 months. Heart disease is a disease with great medications and treatment options, but it does need to be monitored closely.