How does the normal heart work?
The heart is the organ responsible for pumping blood to and from all tissues of the body. The heart is divided into right and left sides. The right side of the heart pumps oxygen-deficient blood returning from the body through the lungs. The lungs re-oxygenate the blood and remove the carbon dioxide waste produced by the body.
After the blood passes through the lungs, it enters the left side of the heart where it is pumped out to the body though the aorta and other arteries.
Each side of the heart is divided into two chambers: an upper atrium and a lower ventricle. Between the atrium and ventricle is a valve: the tricuspid valve on the right and the mitral valve on the left. These valves regulate blood flow from the upper atrial chambers into the lower ventricular chambers. As the heart pumps (squeezes), these valves act as one-way gates that allow blood to flow from the atrium into the ventricle and prevent blood from flowing backwards into the atrium when the ventricle pumps.
The heart pumps blood from the ventricles into the lungs through the pulmonary artery (on the right) or out to the body through the aorta (on the left). The blood flowing through these arteries is regulated by a second series of one-way valves: the pulmonic valve on the right, between the heart and the lung circulation, and the aortic valve on the left, between the heart and the body circulation.
The heart rate (number of heart beats per minute) and the different types of heartbeats are controlled by the electrical system in the heart. Normally, the electrical impulse starts in the upper chambers of the heart (atria), causing them to contract and push blood into the lower chambers (ventricles), which then receive the electrical impulse to contract from the bottom up, squeezing the blood out into the lungs and the rest of the body. Any damage to the heart can affect the electrical system, causing disruption in this carefully ordered contraction. In a normal heart, the heartbeats start in the right atrium, but in sick hearts, the heartbeats can start from any chamber.
What is chronic degenerative valve disease?
Chronic degenerative valve disease (CVD) has many other names, such as endocardiosis, valvular regurgitation, valvular insufficiency, chronic valve disease, and most commonly myxomatous mitral valve disease (MMVD). This disease occurs due to degeneration of the valves between the atrium and ventricle on both the right and left sides of the heart, although the valve on the left side (mitral valve) is typically most severely affected. The degeneration causes the valves to become abnormally thick and develop a nodular, “lumpy” appearance.
The valves become unable to form a tight seal between the atrium and ventricle when the heart is squeezing or pumping. Without a tight seal, the valves leak blood backwards into the upper chambers (atria). The backwards leaking of the blood through the abnormal valve is called “regurgitation” and causes an abnormal sound called a heart murmur that your veterinarian can typically hear with a stethoscope.
This illustration shows the pathway that blood takes as it moves through the heart. The arrows in pink represent blood rich in oxygen, and the arrows in blue represent blood with very little oxygen and high levels of carbon dioxide.
What dogs develop CVD?
CVD represents approximately 75% of all heart disease in dogs. Approximately 60% of affected dogs have degeneration of the mitral valve, 30% have degeneration of both the tricuspid and mitral valves, and the remaining 10% have degeneration in the tricuspid valve only.
The risk of developing CVD increases as dogs get older and is rare before the age of 4 years. In addition, small dogs (weighing less than 40 lb or 18.2 kg) are more likely to get CVD than larger dogs. Certain breeds also have a higher risk of developing CVD.
The general risk factors for developing CVD are:
- Older than 5 years
- Small breed (under 40 lb or 18 kg)
- High-risk breeds: Miniature poodles, cocker spaniels, miniature schnauzers, dachshunds, small terrier breeds, Cavalier King Charles spaniels (this breed may develop CVD as young as 2–3 years of age)
What causes CVD?
CVD is a degenerative process associated with aging. It is not caused by infection. Many older dogs with dental disease also have CVD, but dental disease is not the cause of the CVD. In addition, there is likely an inherited genetic component in some breeds, such as the Cavalier King Charles spaniel, but the genetic evidence for most cases of CVD is lacking.
What happens to a dog with CVD?
The leak (regurgitation) caused by degeneration of the heart valves eventually leads to enlarged heart chambers (the atria and ventricles). Most dogs with CVD feel and act normal; the only evidence that they have CVD is the sound of the leak (heart murmur) that your veterinarian hears when using a stethoscope. This asymptomatic stage is typically called the preclinical stage of the disease (or Stage B1 and B2).
Most dogs with asymptomatic CVD never get sick from CVD, but about a third of these dogs will eventually develop noticeable clinical signs or clues. This development usually happens slowly over a period of years but can sometimes happen quickly.
In general, the bigger the leak, the bigger the heart gets. Eventually, when the heart is big enough, your dog can start to have noticeable problems, such as fast and/or labored breathing, coughing, and other clinical signs (see list below). Clinical signs occur when pressure in the enlarged heart causes fluid to leak out of the blood vessels into the lungs (called pulmonary edema or "water on the lungs") and sometimes leak into the belly (ascites).
The development of clinical signs is referred to as the symptomatic stage of CVD (Stage C). The build-up of fluid in the symptomatic stage is called congestive heart failure. Sometimes, in the symptomatic stage of CVD, the heart cannot send enough blood forward to the body and this can cause dogs to become weak or tired, or even faint.
What are the clinical signs that my dog may have symptomatic CVD?
The clinical signs that occur in dogs with CVD can also occur with other diseases. If you know your dog has CVD, you should always watch for these signs to develop and, if they do, you should contact your veterinarian. It is important to note that not every dog will develop all the following clinical signs, but many dogs will have more than one.
- Rapid and shallow breathing when resting or sleeping (more than 30–35 breaths per minute; for details on how to determine your dog’s breathing rate, refer to the section below about evaluating home breathing rates)
- Increased effort associated with breathing (using abdominal muscles and expanding the chest more)
- Restlessness or agitation while sleeping (e.g., moving around a lot and changing positions due to the inability to find a comfortable position)
- Change in sleeping position (e.g., your dog may no longer sleep on its back or on its side, but more in a sitting or “sphinx” position)
- Coughing or gagging
- Weakness
- Reduced ability to exercise
- Collapse or fainting
- Decreased appetite
- Weight loss
- Distended belly
- Depressed attitude and not interactive
- Gums that appear bluish or pale/white
How can my veterinarian determine if my dog has CVD?
The best screening test to detect CVD in your dog is for your veterinarian to listen to your dog with a stethoscope (auscultation). If your veterinarian hears a heart murmur, they will recommend other tests. If you wish to have your dog “cleared” for breeding, your veterinarian may refer you to a veterinary cardiologist.
What tests might be recommended by my veterinarian once my dog has CVD?
Asymptomatic Dogs with CVD: If your dog is asymptomatic (no clinical signs of CVD are present) and your veterinarian detects a heart murmur, they will recommend further tests to help determine how big the heart is and if your dog should start taking heart medication. Some tests are done to determine if there are any other problems that could be detrimental for dogs with CVD, such as high blood pressure or kidney disease.
Symptomatic Dogs with CVD: A dog with a heart murmur and one or more of the clinical signs listed above could have heart failure, which requires medication. Your veterinarian will recommend tests to help determine the cause of the clinical signs and to help them select the appropriate medications.
Possible tests for dogs with asymptomatic and symptomatic CVD:
- Chest X-rays to evaluate heart size and condition of the lungs and blood vessels
- Blood work to evaluate kidney function
- Urine test to evaluate kidney function
- Blood pressure measurement
- Ultrasound (echocardiogram of the heart) to confirm the diagnosis and evaluate the size and function of the heart
- A blood test called NT-proBNP, which tests for an enzyme released by damaged or “stretched” heart muscle; testing can help determine if a cough is due to heart disease
- A blood test called serum cardiac troponin-1 (C-TnL), another biomarker of heart disease
- Electrocardiogram (ECG) to evaluate the heart rhythm
Referral to a veterinary cardiologist may be suggested in some cases.
How is CVD treated in dogs?
Medication is not required if tests determine that the heart is not enlarged and the blood pressure is normal (Stage B1). If the tests detect heart enlargement and/or high blood pressure (Stage B2 or C), medication may be prescribed.
Can I slow down or reverse the progression of CVD in my dog?
Several studies have looked at preventing CVD from progressing to congestive heart failure. Unfortunately, no drugs tested thus far have proven effective at preventing or slowing the progression of CVD when started at stage B1. At stage B2, starting pimobendan (Vetmedin®), a medication that improves the heart muscle’s ability to contract, may help slow the progression of disease. As new drugs are developed, they will undergo testing, so there may be drugs in the future that could help with CVD progression.
If your dog has symptomatic CVD (heart failure), medications will be prescribed. These medications will likely be continued forever, although the doses and frequency of administration may change over time. Sometimes, additional medications are required, while others are sometimes stopped. Your dog may need to stay in the hospital for a few days while adjusting to the medications. Common medications used to treat heart failure due to CVD include:
- Furosemide, also known as Lasix® — a diuretic designed to make your dog urinate more to reduce fluid in their circulation
- Pimobendan (Vetmedin®)
- Angiotensin converting enzyme inhibitor (ACEI), such as benazepril or enalapril – medications that relax blood vessels, making it easier for the heart to pump
- Spironolactone — another diuretic
Additional medications are frequently prescribed for individual dogs.
Note: Some medications and herbal supplements can have adverse interactions with heart medications, so it is important that you do not use any medications (new or previously prescribed) without talking to the veterinarian that prescribes your dog’s heart medications.
Are there any side effects of any of these medications?
Common side effects of medication used to treat heart failure include:
- Drinking large amounts of water more frequently. It is critical that dogs on medications like furosemide always have free choice access to water.
- Urinating larger amounts more frequently. Dogs always need to urinate within one to two hours of receiving furosemide. To prevent accidents in the house, use a “doggy door” or pee pads, especially if you leave the house for an extended period of time.
- Reduced appetite or not eating normal amounts of food. If your dog eats less, talk to your veterinarian, as it is important that your dog does not lose weight.
What kind of follow-up will my dog need with CVD?
If your dog has asymptomatic CVD (Stage B1 and B2), your veterinarian will recommend recheck appointments every 3 to 12 months, depending on how advanced the disease is. You may need to return 10–14 days after starting a medication to have your dog’s kidney and liver values tested and have their blood pressure taken.
If your dog has symptomatic CVD Stage C (heart failure), your veterinarian will recommend a recheck appointment every 2 to 4 months. In addition, when a new medication is started, you may need to return in 10–14 days to have your dog’s kidney and liver values tested and have their blood pressure taken.
If you notice any of the clinical signs from the list above, at any time, do not wait for the next recheck appointment; call and make an urgent/emergency appointment. If the clinical signs are severe and/or develop suddenly (your dog cannot breathe, rest comfortably or sleep), you may need to go to the nearest emergency facility as soon as possible.
One of the best ways to help your veterinarian determine when to start or adjust your dog’s heart medication(s) is to observe and record the home resting/sleeping breathing rate of your dog.
Why should I evaluate my dog’s resting/sleeping breathing rate at home?
Increased breathing rate while resting quietly or sleeping is an important clinical sign that your dog needs to see your veterinarian: it is an early clue that heart failure is developing because fluid may be accumulating in the lungs. Your observations can help limit how sick your dog becomes, reduce the chances that your dog will ever have to stay overnight in the hospital, and help reduce the costs associated with heart failure treatment.
What is a normal resting/sleeping breathing rate in a dog?
In general, dogs have a breathing rate between 15 and 30 breaths every minute when they are resting calmly or sleeping. This rate occurs in normal dogs as well as dogs with asymptomatic heart disease and heart failure that is well-controlled on medications. Lower rates are possible and are no cause for concern, provided that your pet is otherwise acting normally. It is considered normal for breathing rates to be much higher than this when dogs are hot, stressed, or active.
Resting/sleeping breathing rates that are consistently greater than 30 per minute are increased and considered abnormal. In some cases, rates lower than 30 per minute may be considered increased and abnormal by your veterinarian. Ask your veterinarian what rate is considered increased and abnormal for your dog.
Is there a monitor I can use to track my dog’s breathing?
Yes, there are now sensors that can help you track resting respiratory rates (and resting heart rates) at home. Ask your veterinarian about non-invasive devices you can use for tracking. It is always recommended that you also do your own manual counts to confirm.
How do I count my dog’s resting/sleeping breathing rate?
It is best to wait until your dog is sleeping quietly, but your dog may be resting calmly and quietly. The sleeping breathing rate is typically a little lower than the resting breathing rate.
- Watch your pet’s chest; it moves in and out as they breathe. Count one breath when the chest has moved in and out once.
- Use your watch or phone to time 30 seconds and count how many times your pet breathes during the 30-second period.
- Next, multiply the number of breaths you counted by 2 to get the number of breaths in 60 seconds. Alternatively, you can count the total number of breaths that occur in 60 seconds (1 minute), and then there is no need to multiply.
- Keep a record of the breathing rates you count, such as in a diary or calendar. There are some free smartphone apps that can help you track your pet’s home breathing rate. Search for “dog’s heart resting respiration rate.”
What should I do if my dog’s resting/sleeping breathing rate is increased?
If your dog’s resting/sleeping breathing rate is increased, the first thing to do is to double-check: count the breathing rate a few times over the next couple of hours to ensure the breathing rate is consistently increased. If so, then contact your veterinarian as soon as possible.
Typically, your veterinarian will recommend a recheck appointment in the next day or two so they can adjust medications. If the resting/sleeping breathing rate is increased and other clinical signs are observed, as outlined above, then the situation may be an emergency. In this case, especially if it is after hours, you may need to go to a veterinary emergency center.
How often should I count my dog’s resting/sleeping breathing rate?
Typically, your veterinarian will ask you to count your dog’s breathing rate once per day for a week, while you are learning, so you become comfortable performing this exercise. This frequency also allows you and your veterinarian to learn your pet’s normal resting/sleeping breathing rate.
How often should I check my dog’s breathing rate if he has no clinical signs of heart disease?
Home breathing rates do not need to be evaluated in all pets with asymptomatic CVD. Your veterinarian will tell you if and when it is time to start monitoring the home breathing rate in your pet. In general, it is most important to monitor pets with advanced, asymptomatic heart disease that have a high risk of developing heart failure within the next year. In this case, breathing rates are typically recorded at least once or twice per week. If your dog develops heart failure, your veterinarian may ask you to monitor it more frequently, or even once per day.
How often do I need to check my dog’s breathing rate if he has heart failure?
Home breathing rates should be evaluated at least once per day in all pets that have heart failure and are now receiving medications, such as furosemide.
Can special diets help dogs with CVD live longer?
Some pet food manufacturers have developed heart-specific diets. Some of these diets are severely restricted in salt and some are moderately restricted in salt. Diets that are severely restricted in salt should never be used in asymptomatic dogs with CVD. They may be used in dogs with heart failure if the dog will eat them.
Diets that are moderately restricted in salt (heart-specific diets and most senior diets) can be used in asymptomatic dogs with CVD. These diets are likely not harmful if used as outlined, but they have not been shown to have any benefit, so it is unlikely that your veterinarian will recommend changing your dog’s diet if he is otherwise healthy. It is often beneficial to limit treats that are high in sodium for dogs that have heart disease, especially those in heart failure.
Are there any dietary supplements that may help dogs with CVD live longer?
Supplements are unlikely to be harmful if used as outlined by a veterinarian who is familiar with all the medications your dog is receiving and the type and severity of heart disease your dog is suffering from. In most cases, there is no proof that your dog needs to take any supplements if he is on a high-quality commercial dog food diet.
The most common supplement recommended in dogs with CVD is omega-3 fatty acids. Be sure to talk to your veterinarian about any supplements your dog receives, or any new ones you wish to start.
Should my dog exercise if he has CVD?
In general, dogs with both asymptomatic and symptomatic CVD should be allowed to exercise at their normal level if they want to, but the duration of sustained strenuous activities (e.g., ball retrieval, swimming, Frisbee) should be limited, especially in hot or cold weather. Some exercise is good for your dog, and part of what helps your dog enjoy life.
Is there a surgical treatment option for dogs with CVD?
In human medicine, it is common for patients with significant CVD to have the leaky valves repaired or replaced by a surgeon. This treatment requires open-heart surgery and cardiopulmonary bypass, which is a very difficult surgery to perform on dogs, especially small dogs. For that reason, open-heart surgery and valve replacement or repair is not readily available for dogs.
A few veterinary surgeons have performed these surgeries on a very limited number of dogs. There is a very high risk of death, and the surgery is very expensive, so this option is not currently recommended.
If you wish to investigate the possibility of surgical repair or replacement, talk to your veterinarian. In the future, catheter-based (minimally invasive) techniques may become available and allow repair or replacement to be done safely, without the need for cardiopulmonary bypass. Heart transplantation is not an option in dogs.
How long will my dog live now that he has CVD?
Asymptomatic CVD (Stage B1 and B2): On average, most dogs with asymptomatic CVD will live for many years (1–5 years or longer) without ever developing any clinical signs of heart failure. Some will develop clinical signs of heart failure as outlined above and it can be difficult to determine how an individual dog’s condition will progress, so this is why your veterinarian recommends tests and recheck appointments.
Symptomatic CVD (Stage C or Heart Failure): Once your dog develops clinical signs of CVD, medications can typically eliminate or reduce the severity of the clinical signs, but the disease will progress, and eventually the medications will not work as well. Sometimes, new medications can be added or the doses of your dog’s current medications adjusted, but eventually, this will be insufficient in maintaining your dog’s quality of life. Your veterinarian will help you recognize when and if this is the case for your dog. In general, with the appropriate medications and recheck appointments, many dogs with heart failure due to CVD live for one to two years or even longer.
