Dog heart failure is a serious condition. The heart is responsible for pumping blood to all corners of the body, therefore is considered a vital organ. Fortunately, you can identify some dog heart failure symptoms that may help you make better decisions to help your pet friend.

What we will cover in this article:

What is heart failure?

How frequent is heart failure in dogs?

What other factors predispose dogs to have heart failure?

What is the progression of dog heart failure?

What is the outcome of dog heart failure?

What are dog heart failure symptoms?

Some symptoms explained

What other symptoms a dog with heart failure will have?

What sounds can normally be heard in a dog’s heart?

Where to listen to a dog’s heart?

How to check a dog’s heart rate?

What are heart murmurs?

How heart failure affects dogs

What is a heart attack? Do dogs have heart attacks?

How to prevent heart failure in your dog?

What is the best diet for a dog with heart failure?

What is the right level of activity for a dog with heart failure?

How do you treat a dog’s heart disease? Common medication

Final remarks

What is heart failure?

Dog heart failure occurs after heart disease have been in an ongoing course already for a while

The most frequent heart disease in dogs is dilated myopathy, the most common cause of heart failure.

In this disease, the heart’s muscular walls become thin and weak. Therefore, the heart cannot cope with pumping blood to all the rest of the body.

Luckily, not all dog heart diseases lead to heart failure.

This is what a dog heart looks like:

How frequent is heart failure in dogs?

Around 1% in the dog population, but can be up to 4 times higher in older dogs and in certain breeds

What are the breeds predisposed to suffer from dog heart failure?

Dog breeds more commonly suffering from heart failure due to heart disease include Doberman pinschers, Boxer, Great Dane, Scottish Deerhound, Irish Wolfhound, and Cocker Spaniels.

What other factors predispose dogs to have heart failure?

If your dog is 4 to 10 years old and male, he will probably have a higher chance of having heart failure.

What is the progression of dog heart failure?

In some cases, heart disease, especially if untreated will progress to death. Here is a simplified overview of the progress of heart disease in dogs:

  1. Heart disease develops silently
  2. Heart failure starts
  3. Symptoms appear
  4. Sudden death (in some cases, see outcome below)
Milestones of dog heart failure: heart failure starts (silently) - heart failure develops (symptoms appear) – heart arrhythmia – death
Evolution of heart failure in dogs. Dog heart failure develops gradually. Dog heart will go through changes or milestones like when the heart muscle walls begin to thin (heart failure starts). When these changes are severe enough, dogs will show symptoms like fatigue, low activity, and respiratory distress. Dogs may even collapse. Arrhythmia (disorganized heartbeat) is the main cause of death in dogs with heart failure

What is the outcome of dog heart failure?

As mentioned in a study, “the duration of clinical signs before referral is often short” (about three weeks) and “the survival times are poor” that is a little less than five months, Doberman dogs being one of the breeds with that low survival time. Some dogs may survive as long as two years after being diagnosed with heart failure if appropriately medicated and with a good quality of life.

What are dog heart failure symptoms?

A dog with a failing heart will show the following symptoms:

  1. Decreased activity
  2. Lethargy (always sleepy or laying down)
  3. Weakness
  4. Fatigue (your dog becomes tired even after a short period of exercise, also called exercise intolerance)
  5. Collapse or syncope
  6. Difficulty to breath
  7. Cough
  8. Abdominal distension (swollen belly)
  9. Weight loss
  10. Anorexia (loose interest in eating)

When owners take their dogs to the veterinary clinic, the most common signs are breathlessness and coughing.

Some symptoms explained

Now let’s go a little more into detail about these symptoms and why they develop.

Decreased activity

When a dog’s heart starts to fail, the heart cannot pump blood to all the tissues in the body. Thus, nutrients and oxygen become more scarce for cells to produce energy. As a result, your dog will look tired and not be very interested in walking or playing.

Exercise intolerance

Dogs with exercise intolerance have a low exercise capacity meaning a low ability to endure exercise in level or duration.

Animals with heart failure often cannot have enough blood circulation to sustain increased activity levels. Consequent changes that occur over time impair blood flow into muscles during exercise and contribute to reduced exercise tolerance. Your dog may look tired or reluctant to engage in activities they no longer enjoy.

Collapse or syncope

Dogs that go into a syncope will become temporarily unconscious and lose general muscle tone (therefore collapsing).

A syncope occurs because as the heart fails, insufficient oxygen or glucose will be delivered to the brain. Vets will rule out the possibility of seizure episodes as they look similar to a syncope.

Usually, a syncope episode in your dog will be preceded by a physical effort (like walking fast or in hot weather) or excitement.

Micturition or vocalization (as if being in pain) is not uncommon.

Note that collapse or syncope is not a “heart attack.” It is more like fainting. This shouldn’t be confused with a “heart attack” (see below).

Syncope can be confused with seizure episodes. Vets can differentiate among other conditions that make a dog collapse.

A reduced oxygen supply causes syncope to the brain because of a faulty heart. Before the collapse, when reduced oxygen supply to the brain is not severe enough, a dog may enter a short shakiness or weakness phase, particularly in the rear limbs.

Dog lying down with heart failure and syncope. Syncope is a temporary loss of consciousness and muscle tone
Dogs with heart failure will often have syncope episodes. Syncope is a temporary loss of consciousness and muscle tone that precedes situations of physical effort and excitement in dogs with heart failure symptoms. Syncope is a distressing and often scary symptom of heart failure in dogs. Our “actor” dog Spanky isn’t dead or anything. He is just playing dead, just in case you were wondering! Look at his waving tail =)

Difficulty to breath

Veterinarians call this symptom dyspnea.
Why do dogs with heart failure have difficulty breathing?
Among the common diseases causing heart failure are dilated heart disease (or dilated cardiomyopathy) and chronic valvular heart disease.
Dilated cardiomyopathy occurs predominantly in medium to large breed pure-bred dogs, usually breeds with more than 15 kg body weight. Great Danes are particularly predisposed to dilated cardiomyopathy (almost 4 out of every 10 Great Danes).
When the heart becomes dilated, the heart walls become thinner (and weaker). The heart valves become open (when they should be closed), resulting in the blood flow going back to the lungs and other parts of the body. The right valve leading from the auricle (upper chamber) to the ventricle (lower chamber) is usually compromised in dilatated heart disease, explaining the blood leakage back to the lungs. When this happens, the lungs cannot work correctly, and blood is not properly oxygenated. Besides, the heart weakness impedes pumping enough blood to the lungs for reoxygenation.

Image showing the normal and abnormal (as in dogs with symptoms of heart failure) flow of blood in the heart
Normal functioning: when the heart contracts, it pumps blood into the arterial system. Two main arteries come out of the heart. One goes to the lungs (pulmonary artery) that carries blood to be oxygenated there, and one goes to the body’s general blood circulation (aorta artery). Once the blood has traveled the body, it returns to the heart through veins. Blood flows into the heart through the atria (upper compartments) and from the atria to the ventricles. From the ventricles, the blood passes to the arteries, repeating the cycle over and over again. The heart valves ensure that blood follows the flow in a normal direction and that it does not return backward (yellow arrows). 
Abnormal functioning (heart failure): the heart valves are affected by several diseases. In dilated heart disease in the dog, the heart’s walls get thinner, which causes the valves located between the atria and ventricles to become a little open during each cycle of contraction of the heart. These minor valve defects are heard in the form of murmurs and cause blood to return (green arrows) from the ventricles to the atria and from these to the heart’s veins. If blood, instead of passing from the veins to the heart (as it should be), does the opposite, there will be an abnormal blood flow to the lungs (congestion and cough) and the abdomen (swollen or distended belly).

To make things worse, the left side of the heart cannot pump enough blood to the body. As a result, the respiratory center in the brain becomes depressed and commands to lower breathing frequency.

The situation can become harsh for a dog under these conditions, so much that they may need to separate their forelimbs wide open to widen the thorax in an effort to inhale more air.

Dogs will sometimes need to breathe with an open mouth because the air going through the nostrils is insufficient.

Cough

Respiratory effort irritates the airways initiating the reflex of cough.

Cough is also produced because when heart failure occurs, heart valves become faulty, allowing an abnormal backward blood flow to the lungs, creating congestion.

Cough in dogs with heart failure occurs after exercise and is usually worse at night.

What other symptoms a dog with heart failure will have?

We have been covering symptoms you may notice at home, but your veterinarian will discover other symptoms upon careful examination, like:

  • Murmurs
  • Altered electrocardiogram
  • Altered ultrasound and X-ray images of the heart

Murmurs (Listening to a dog’s heart)

Can be detected through a hearing medical device you may be familiar with, a stethoscope

Stethoscopes are used for the diagnosis of dog heart failure. Symptoms may include murmurs, usually found during heart failure
Image courtesy of Manik Roy from Unsplash

However, if you do not have a stethoscope, you can hear your dog’s heart by placing your ear against the dog’s thorax.

Where to listen to a dog’s heart?

To answer this, we first have to consider where is the dog’s heart located.

The dog’s heart is slightly tilted to the left, so the left side is the best to listen to heart sounds in the face of suspected heart failure.

The right place to begin with to listen to a dog’s heart is in the lower chest side wall, right behind the left elbow.

Image showing the normal position of the dog's heart. It is located in the lower part of the thorax, right behind the elbow.
The dog’s heart is located in the lower chest (thorax), right behind the left elbow. About 2/3 of the dog’s heart is located to the left of the middle line. That is why it is best to listen to heart sounds on the left side of the thorax.

You will hear a series of sounds like lub followed by a dub, repeated endlessly. The lub part is produced when the heart contracts (called systole), and the dub occurs during the rest phase (called diastole). Technically, the sounds are produced when the heart valves close (The atrial-ventricular valves make the lub sound, and the arterial valves produce the dub sound).

These sounds are normal. However, when you can hear the heart sounds all over the chest walls, this means your dog’s heart is probably enlarged and in the process of heart failure

How to check a dog’s heart rate?

The pace of the series of sounds determines the heartbeat frequency. You can hear the heartbeats by placing your ear in your dog’s chest (behind the elbow, on the left side). Try to do this in a quiet place when your dog is calmed.

You can count the number of heartbeats for 15 seconds and multiply that number by 4

Adult dogs at rest usually are in a rate of 60 to 160 beats per minute (slower in large

dogs and faster in toy dogs.

Puppies have a high-speed heart rate (as much as 220 beats per minute).

A remarkably fast frequency may be a sign of:

  • Anxiety
  • Fever or infections
  • Anemia
  • Blood loss
  • Dehydration
  • Shock
  • Heatstroke
  • Heart disease

A slow pulse is a solid sign of heart disease

Heart arrhythmia is a condition in which heartbeat frequency becomes irregular or disordered.

What are heart murmurs?

Heart murmurs are another kind of heart sound. Murmurs are one of the common abnormal sounds found by a veterinarian and are usually found in dogs with heart failure. In the UK, nearly 4% of the dogs visiting the veterinarian will have heart murmurs.

They are a slight shhhhh or like a whooshing sound. This sound is made when heart valves are too narrow (stenosis) or do not close properly, causing a backflow of blood to the previous chamber of the heart. In both cases, blood flow becomes disordered (turbulent), as in a roaring current of water in a river. Some are very subtle and not serious (innocent). In other cases, murmurs are signs of heart disease.

The two common diseases causing heart failure (dilated cardiomyopathy and chronic valvular heart disease) produce murmurs.

Your veterinarian may indicate a chest X-ray, an electrocardiogram (ECG), and an echocardiogram to know whether a murmur in your dog is associated with heart disease.

Altered electrocardiogram

The electrocardiogram (ECG) is an exam to study the heart’s regular electrical activity. Electrical activity always precedes muscle heart contraction. In dogs with heart failure, the electrocardiogram pattern will be altered. Let’s see first what a typical electrocardiogram pattern is like.

A heartbeat is represented by a pattern in an electrocardiogram composed of waves. An electrocardiogram study will show a repetition of these patterns (each pattern = one heartbeat). Each pattern will look like this:

Dog heart typical pattern of a electrocardiogram

Each pattern has several waves:

Basic pattern of heart muscle contraction in the dog ECG. P, Q, R, S, and T represent electrical events during the heart's contraction cycle.

Each wave represents a part of the whole heart contracting cycle. What happens first is that the heart pacemaker (called the sinoatrial node) generates an electric impulse that travels through the heart muscle tissue of the upper part of the heart (atria). This is represented in the electrocardiogram by the P wave. Then the electric impulses travel down through the lower chambers of the heart (ventricles), represented by the QRS wave. This complex is active during ventricle contraction to pump blood to the body (left ventricle) and the lungs for oxygenation (right ventricle). Finally, wave T is the recovery wave to prepare the heart (electrically) for the next beat.

An arrhythmic heart electrocardiogram may look like this:

An arrhythmic pattern of atrial muscle contraction in the dog ECG. Small disorganized spikes come after the QRS complex, representing fibrillated electric signals in the atrium of the dog's heart
An arrhythmic pattern of atrial muscle contraction in the dog ECG (notice the high frequency of repetition of patterns and the absence of the P wave)

Or even (and worse) like this:

An arrhythmic pattern of heart muscle contraction in the dog ECG. Big high amplitude, disorganized spikes can be seen and not recognizable QRS complex and the accompanying waves can be seen, representing fibrillated electric signals in the ventricle of the dog's heart
An arrhythmic pattern of heart muscle contraction in the dog ECG (ventricles)

Altered echocardiogram (ultrasound) images of the heart

Ultrasonography is an imaging technique that uses high-frequency sound waves (ultrasound) to produce images of body organs.

Most dogs with heart failure will have arrhythmia when arriving at the veterinary clinic and radiographic and ultrasound signs of an enlarged heart and liquid accumulation in the lungs and pleura (the space surrounding the lungs).

This is an echocardiogram made with ultrasound technology
This is an echocardiogram made with ultrasound technology

How heart failure affects dogs

Heart failure affects the quality of life of your dog. They will require medication, lifestyle changes, and special dog heart diets. The aim should be to provide your dog with the best possible care. Heart failure can be considered a chronic disease, so having a good quality of life for your dog should always be kept in mind. Enrichment of the environment to make things easy for your dog is essential. For instance:

  • Placing ramps for bed access
  • Locating bed and feeding space downstairs
  • Reduce general stress at home
  • Avoid major routine changes for your dog with an ailing heart

What is a heart attack? Do dogs have heart attacks?

The leading direct cause of death for dogs with failing heart is arrhythmia. The heart muscle has the function to contract to pump blood and, at the same time, conduct electric impulses to coordinate this contraction. Arrhythmia is an irregular heartbeat

Dogs with heart failure symptoms may develop arrhythmias that mess up the electrical signals within the heart to the extent that the heart stops beating. Arrhythmias occur at the final stages of the process of dog heart failure.

This been said, when your dog suffers from heart failure and collapses or suddenly drops unconscious, it could be a sign that they are having a heart arrhythmia or fibrillation (what we humans would call a “heart attack” or wrongly a “heart failure”). The results are similar, but the causes are somehow different.

Then you probably wonder what a heart attack in humans is. It usually means that heart muscle areas die because of the absence of blood supply. This is usually called infarction, and the lack of blood usually comes from blocked coronary arteries (the blood suppliers for the heart).

In that case, you should cover your dog with a blanket, straighten the head and neck to free the airways, and immediately contact the veterinary emergency service.

Veterinarians have special defibrillation equipment to attempt restoring regular heart beating after an arrhythmic or fibrillation episode. Human defibrillators cannot be used because the energy they release is too high for small animals (like dogs and cats), for which special veterinary equipment exists.

Image depicting the heart's normal electrical current flow for coordinated contraction and what happens with these currents during abnormal (arrhythmia) heart functioning in dog heart failure
Heart movements are coordinated by electrical impulses (green arrows) initiated automatically in the heart’s natural pacemaker, located in the upper wall of the right atrium). Electrical impulses run through the heart septum (the wall that divides the heart into right and left halves) and from there to most of the heart muscle. During arrhythmia (the final event of a dog heart failure, potentially deadly), the electrical impulses become disorganized, the heart contracts in messy patterns and may eventually stop

How to prevent heart failure in your dog?

You can proactively strengthen your dog’s heart following some simple preventive actions.

Some preventive measures are:

  • Predisposition
  • Exercise
  • Body condition
  • Nutrition

Predisposition

Well… this is not actually a measure but something really important that you should consider. Be aware of the factors that might predispose your dog to suffer from heart disease. Your veterinarian will give you the best advice to take action in advance if you have a dog that will most likely develop heart disease. That way you will be prepared before the disease even develops. See predisposition for your dog to suffer from heart failure.

Exercise

A dog that grows as an athlete at a young age will have less risk of developing heart failure. Daily exercise assists with your dog’s optimal heart and blood vessel health. Exercise promotes a higher blood flow through the heart, promoting heart muscle building and endurance. Therefore, the heart becomes more resistant, and your dog can have a long life with an adequate quality of life. If your dog has been diagnosed with heart disease see below in the article for some tips on the proper way to get exercise.

Body condition

Overweight dogs are those with a body condition above the average. Obese dogs are dogs with a body condition to the extreme right of the score and usually show organ disease and failure because of the associated metabolic stress.
Overweight dogs are at risk for heart disease, and obese dogs are even more.

Diet and supplements

Some commercial food contains ingredients that can aggravate heart conditions, particularly those with high fat, low-quality protein, and high salt content (Sodium). In addition, many of these ingredients can produce a general inflammatory condition in the body that may adversely affect your dog’s heart.
Some specific diets may pose a risk to your dog and increase the chance of producing heart dog failure.

Recommended commercial food and supplements are available to promote a healthy heart in your dog

What is the best diet for a dog with heart failure?

Your Vet will probably reduce dietary Sodium below 12 to 15 mg/kg daily, mostly if cardiac symptoms are severe. However, a strong Na + restriction is unnecessary when your dog is medicated. Your Vet or veterinary cardiologist will advise well about this.

Commercially prepared diets are best for feeding dogs with heart failure.

What is the right level of activity for a dog with heart failure?

Allow your dog to choose its own level of activity. Avoid strenuous exercise as this will lead to collapse or sudden death. You will have to reduce the <exercise time from the standard for the breed>.

Dogs with heart failure should be monitored when exercising, especially during hot or humid weather.

How do you treat a dog’s heart disease? Common medication

Your Vet will advise you on the best way to medicate your dog with heart failure.

Except for severe cases of dog heart failure, your veterinarian will prescribe medications that can be given to your dog at home.

Suppose your dog has suffered collapse (syncope) or is brought back to life after an arrhythmia episode. In that case, your Vet will stabilize the patient first (probably making sure the arrhythmia is not present anymore, the kidneys are working correctly, and the body temperature is back to normal by warming up your dog). At this stage, oxygen and fluids may be administered depending on the severity of the condition and whether the lungs are having congestion.

Depending on the exact heart problem your dog may be facing, your vet will carefully choose the best specific drugs to administer to your dog.

Your vet will choose a specific combination of drugs from the following list:

Diuretics (help your body to eliminate sodium and water through urine, thus reducing the amount of water in the blood that your dog’s heart has to move)
Examples: Furosemide, Torsemide, Spironolactone, Chlorothiazide, Hydrochlorothiazide

ACE Inhibitors (Angiotensin-converting enzyme or ACE inhibitors help relax the veins and arteries to lower blood pressure, thus easing the job of your dog’s heart)
Examples: Enalapril, Benazepril, Captopril, Lisinopril, Ramipril, Imidapril

Vasodilators (similar function as ACE inhibitors)
Examples: Hydralazine, Amlodipine, Prazosin, Nitroglycerin ointment, Isosorbide dinitrate, Isosorbide mononitrate

Positive Inotropes (raise the heart strength, reducing the effort to pump blood)
Examples: Pimobendan and Digoxin

Final remarks

Dog heart failure is a serious condition as it can lead to death and unpair normal life for your dog

Heart failure shouldn’t be confused with a heart attack occurring in humans. Heart failure in dogs is a slowly developing chronic condition that will lead to heart arrest and dead for different reasons than for humans. That is, heart failure in dogs is not a moment or an event but rather the course of a disease. Heart murmur (a usually abnormal heart noise) is a common symptom of heart failure.

The most common disease in dogs where heart failure develops is dilated canine cardiomyopathy (DCM).

Dog heart failure should be closely monitored by a veterinarian or veterinary cardiologist

As dog heart disease cannot be reversed, we owners should make sure our dogs live the best possible life.

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