Like all mammals, dogs and cats have a four-chambered heart. It consisting of a left and right upper chambered atrium and a left and right lower chambered ventricle.
The left and right atria receive blood from the lungs and body respectively. The left ventricle is responsible for pumping oxygen-rich blood from the lungs out through the aorta into the body, while the right ventricle pumps the blood through the pulmonary artery to the lungs for oxygen.
The heart has 4 one-way vales to keep blood flowing in the right direction. The valve between the left atrium and ventricle is the mitral valve. The one between the right atrium and ventricle is the tricuspid valve. The one regulating blood going into the aorta is the aortic valve and the one regulating blood going to the lungs is the pulmonary valve.
The mitral valve is the most fragile of the four valves in your pet's heart. In dogs, it is often the first one to wear out.
The first sign that most owners notice is a cough. this is because enlarged, failing hearts allow fluid to back up into the lungs and also press on the wind pipe.
Other signs you may notice in your pet are tiredness, rapid breathing, poor appetite, an enlarged tummy, pale or bluish gums, and a rapid, weak pulse. Fainting is less common.
Many of these pets have heart murmurs. Heart murmurs come about when a passage through the heart becomes too narrow or too wide. In middle aged or older adult cats and dogs, this usually means that a valve is not working properly. It may not be closing sufficiently or it may not be opening sufficiently. In younger pets, a murmur might mean that the heart did not develop properly.
Anemic pets develop heart murmurs because their blood is too thin (anemic) - not because of an abnormal heart.
The rhythm of a weakened heart also changes. But unlike us, frequent changes in the heart rate of relaxed dogs is normal.
If your veterinarian is suspicious that your dog might have a heart problem, the first test we traditionally do is an x-ray. If the x-ray shows an enlarged heart, your veterinarian may be satisfied with that and begin treatment.
If it is unclear if your pet's heart is enlarged or if its heart is even the source of its problems, a proBNP test might be ordered. (ref) This test is especially useful in cats when we are not sure if the cat has a lung problem, asthma or a heart problem.
Other tests that your veterinarian or a cardiac specialist might perform are echocardiograph (doppler ultrasound) to see the heart perform in real time, and an EKG to check if the electrical system of the heart is functioning normally.
In dogs, the valves are often the first heart structures that are affected. Heart disease in cats usually involves the entire heart muscle and not just the valves.
Dogs let us know early that there is a problem. But we are often unaware that our cat has a heart problem until its heart is well on its way to failing. Often the only signs in your cat are weight loss, and difficulty breathing. Cats are more likely to make asthmatic-like sounds than to have a hacking cough.
Cats with this form of heart disease do not survive long. Signs of all forms of heart disease in cats are quite similar and your veterinarians will not be able to tell one from the other without some sophisticated tests.
In all cases of heart disease in dogs and cats, as the circulatory system fails, the kidneys liver and all other organs are flooded with stagnant blood and work inefficiently. This is because they do not get the oxygen they need.
The heart is like your car's motor. If one part goes out, it is not long before it causes another part to fail. So in reality, most actual cases of heart disease are a combination of several problems. The normal heart has a very precise shape. As its shape expands and becomes more rounded, the heart is not able to perform any of its tasks well.
Congestive heart failure is the result of an enlarged heart - one that allows blood to abnormally pool (congest) and move sluggishly throughout the body. No mater what the underlying heart problem may be, CHF is often the end result. You can read about how the problem affects dogs here. The problem is less common in cats, but when cats develop CHF, how it affects their bodies is quite similar.
CHF occurs when the heart is unable to meet the circulatory demands of the body. Many things can cause the heart to be faced with increased back pressure and decreased effectiveness as a pump. Valvular defects, tumors, heartworms, heart beat abnormalities, and damaged to the muscle itself all cause the heart to enlarge and blood to pool in the organs and lungs. The net effect of all this is called congestive heart failure.
All pets with CHF have an enlarged heart. As the disease progresses, the normal triangular shape of the heart becomes rounded. This is very noticeable on an x-ray. An x-ray or a cardiac ultrasound is the way your veterinarian will confirm CHF.
Since CHF is a common human problem, drugs are constantly being developing and refining to treat it. These human medications work quite well in our pets too. So your veterinarian may be using a drug I have not mentioned. This is particularly the case if you visit a veterinary cardiologist. However, it is uncertain if these newer human medications extend the life of your pet any more than those that are more commonly used by your local veterinarian.
We remove as much pooled fluids and blood as we can with drugs called diuretics. Once these fluids are removed from your pet's lungs, the cough should go away or be much better. The big pot-belly associated with CHF should also go away. The most commonly used diuretics is furosemide (Lasix).
When furosemide will no longer remove enough fluid from your pet, we often add a second diuretic called spironolactone.
Do not be surprised when your pet drinks and urinates more on those medications.
We also increase the diameter of blood vessels throughout the body with vasodilator drugs so the heart does not have to work as hard. Most of the medicines of this group are called ACE inhibitors. The most common ones in this group are enalapril (Enacard) and Lisinopril (Prinivil).
By making it easier for blood to flow through blood vessels, ACE inhibitors help decrease your pet's heart rate, and help preserve the heart's remaining strength. The most common side effect of these drugs is lack of appetite and vomiting. If that occurs, the dose needs to be adjusted.
Inodilators (positive inotropes) are a group of drugs that seem to definitely extend the lives of dogs and cats with CHF. The one most commonly used is called Pimobendan (Vetmedin). It increases the amount of blood that the weakened heart can pump by giving more strength to its muscle fibers. It also opens up blood vessels throughout the body so the heart doesn't have to work as hard. A study found that dogs receiving pimobendan and furosemide lived 9 months longer than those receiving only enalpril and furosemide. It has been used in cats, although it is not licensed for that species.
A drug in this group that was quite popular is digoxin. Because of its potent side effects and the limited length of time pets will survive while on it, I rarely prescribe it. It is a medication of last resort.
The heart has an electrical wiring system to coordinate it's contractions. When the heart is damaged, this system may fail. We call the abnormal beat rhythm a cardiac arrhythmia.
Some of the drugs used to control arrhythmias are propranolol (Inderal) procainamide (Pronestyl), and tocainide (Tonocard).
Many veterinarians suggest pets with heart disease consume a low sodium diet. This is a particularly good idea if your pet also has elevated blood pressure or retained fluid. We do not know if low sodium diets are as beneficial to pets as they are to humans.
Some veterinarians prescribe coenzyme Q because of its beneficial effects in people with dilated cardiomyopathy.
Omega-3 fatty acids are high in fish oil. In people, there is some evidence that omega-3 supplements might reduce the risk of heart attacks and strokes. Based on this, some veterinarians suggest that dogs with heart problems also receive them.
L-carnitine is involved in the process by which the heart muscle converts fats into energy. There is some data that L-carnitine supplements help people who have heart disease. Whether or not it helps pets, we do not know.
There is a small group of dogs and cats that develop heart disease due to a deficiency in the amino acid, Taurine. Since it is non-toxic, some veterinarians suggest a taurine supplement for all their cardiac patients.
Keep your pet's weight optimal, feed a name brand high quality commercial diet or prepare one at home. (ref)
In exercising your pet, keep activity to a level somewhat less than what it would take to cause your pet to breath heavily, pant or elevate its heart rate. Don't give up short walks until you absolutely must. Dogs and cats benefit physically and mentally from activity.
Certain breeds of dogs, particularly toy breeds, have a tendency to develop scaring heart valve problems or endocardiosis. This is the most common form of heart disease in dogs and the rarest in cats.
Age-related scaring of the mitral valves is also quite common in all old dogs. The mitral valve divides the lower and upper left chambers of the heart. It's constant hard work may cause it to fail to completely close and open. Sixty percent of dogs over 8 years old have some degree of this problem. But less than half the dogs with this condition have any symptoms you will notice.
Many veterinarians have noticed that small breeds of dogs that eat soft food and table scraps eventually develop chronic mouth infections or periodontal disease. It is very common for these pets to also have a heart murmur related to their mitral valve. We think that bacteria move from the infected gums through the blood and attach to the heart valves to cause a condition called endocarditis that eventually scar the heart valves.
When the mitral valve wears out, its two flaps become blunted, shriveled and scarred so that they do not open or close properly. When this happens, blood does not flow in the normal pattern but leaks back in to the atrium or ventricle.
With time, increased back pressure causes one or more chambers of the heart to enlarge. As the chambers of the heart enlarge they press on the windpipe resulting in a dry, hacking cough. The enlarged heart also stretches the nerve fibers that control heart rhythm resulting in abnormal beats or arrhythmias. As blood backs up, it pools in the lungs as edema that makes the cough even worse. Particularly when the pet is lying down or at rest.
Dogs and cats are sometimes born with abnormal hearts. We call this congenital heart disease.
This problem is most common in big dogs (Rotties, Boxers, Newfoundlands, Goldens, Great Danes etc.) It is the most common inherited heart disease in large dogs.
In subaortic stenosis the puppy is born with an abnormally narrow passage way leading from the heart to the aorta. It comes in all degrees, from a very mild case, requiring no treatment to a life-endangering problem.
When you take a puppy to the vet for his first vaccinations, the veterinarian should listen to the puppy's heart. In a puppy with SAS, there will usually be a heart murmur over chest near the left base of the heart. If the puppy is not severely anemic with hookworms, then SAS is the most common cause of the murmur. This is how most cases of SAS are first diagnosed. Not every puppy with a heart murmur has SAS. Puppies often outgrow heart murmurs without our really knowing what caused them in the first place. Only some complicated tests can tell which murmur is important. But if your puppy still has a murmur when it is 6 months old, SAS becomes likely.
When a puppy has a significant degree of SAS, its heart has to work harder to force the blood through the narrow area just below the aortic valve. With time, the heart muscles get thicker due to the extra effort. As the walls thicken, the full heart holds less and less blood and needs more and more oxygen. Eventually, the heart begins to fail. Unlike older dogs with CHF, SAS puppies often die suddenly when clots form in the heart muscle or its electrical system fails.
Neither parent of an SAS puppy should ever be bred again.
Most often, you will see no signs at all in your puppy. But as time goes by and the puppy's heart muscles thicken, problems in the electrical system of the heart can cause fainting or unexpected sudden death.
What Tests Might My Veterinarian Perform ?
To decide how serious a heart murmur really is, your pet needs to have an echocardiograpy (doppler ultrasound) performed by a veterinarian experienced in interpreting the results. An x-ray and an EKG will also be required to see how much damage has already occurred.
The most popular drugs used to treat SAS are known as beta blockers (ß-blockers). The most commonly used ones are Propranolol (Inderal) and atenolol (Tenormin). Beta blockers reduce heart rate, help control abnormal heart rhythm and reduce blood pressure. They are proven in their ability to extend the lives of dogs with SAS.
Open heart surgery to correct this problem in dogs has not been as successful as one might hope. Dogs that have had the surgery, live about as long as dogs that just receive medicine.
This technique is similar to balloon angioplasties that are done to dilate blocked coronary arteries in people. A catheter is threaded into the heart and a balloon is expanded in the narrowed area of the heart. So far, this technique has not led to increased life span.
This is very difficult to predict. They younger the puppy is when the problem is first noticed, and the louder the heart murmur, the bleaker the outlook. Most dogs with the typical signs of SAS do not live over 3 years without medication.
A cardiac work-up at a regional veterinary center that includes all the diagnostic tests, might give you more insight. But all pets with this condition can die suddenly - and often do.
This problem was due to a deficiency in an amino acid, taurine. Now that we know that cats must have sufficient taurine in their diet, all major brands of cat food have adequate taurine levels.
Taurine deficiency caused the heart muscle to loose its strength. Cats with this problem lost weight and had difficulty breathing. Blood clots often formed in the hearts of these cats.
A second, genetic form of the disease occurs in Siamese, Burmese and Abyssinian cats. We treat this condition with the same medicines that increase the hearts efficiency and decrease pooled fluid in the lungs. We also give them drugs to reestablish their normal heart rhythm. Many veterinarians include a taurine supplement in any heart condition in cats. A similar heart disease can also occur secondary to an over-active thyroid gland. Cats with this problem will not live very long.
Read about this problem here. In this disease the walls of the heart thicken, leading to inefficient pumping of blood. Blood pressure rises and fluid accumulates in the lungs. Eventually the chambers of the heart enlarge and abnormal heart rhythms occur. Signs of this disease are labored breathing, rapid heart rate, heart murmurs, weakness, collapse and death. Rare heart valvular disease, hyperthyroidism and asthma can mimic hypertrophic cardiomyopathy. We diagnose this disease with x-rays electrocardiograms (EKG = ECG) and cardiac ultrasound.
In this condition localized scarring of the heart muscle prevents the normal beating of the heart. This leads to an enlarged, weak heart and congestive heart failure. Signs of the disease are poor appetite, weight loss and difficult respiration. Sometimes blood clots that cause paralysis of the limbs occur. X-rays, EKG and ultrasound all show atrial enlargement. We treat these cats with calcium channel blockers such as diltiziam, diuretics such as furosemide and low doses of aspirin. Aspirin must be used with extreme caution in cats - if at all . Do so only under the supervision of your veterinarian. Low sodium diets might also help if the pet will eat them. If cat owners are fortunate, a cat with this disease might live an additional year.
In 2004, the University of Minnesota Veterinary Center noticed an occasional link between heart failure and a recent dose of a number of corticosteroid medications in their feline patients (particularly with injectable methyl prednisolone acetate = Depomedrol aka "Depo"). Of the 160 cats with heart failure that passed through their clinic between 1992 and 2001, at least 8% that developed congestive heart failure had received those medications within the 1-3 weeks preceding their developing heart problem symptoms. This unique form of heart disease often resolved itself with time. Corticosteroids are often given to cats with respiratory problems that are believed to be asthmatic. In other cases , they were given for allergic skin conditions or as appetite stimulants. (ref)
Read more about this heart problem here. In this condition, as in cats, the heart chambers enlarge to the point where they can no longer pump blood efficiently. It is most common in large breeds of dogs and rare in small breeds. Doberman Pinschers, Great Danes, German Shepherds and Labrador Retrievers are particularly at risk. The disease is most common in middle-aged dogs, especially males. Usually the cause is unknown. However, we think that taurine deficiencies, parvovirus and the use of adriamycin have all caused the disease.
The overly-stretched heart muscle that occurs in this disease is an inefficient pump. Signs of the disease are those of congestive heart failure: difficult breathing, weakness, coughing and fluid enlargement of the abdomen. These dogs may need oxygen until medicines have an opportunity to work. Low salt diets as well as supplements that contain taurine, L-carnitine (carnatine) and coenzyme Q may also be helpful. Dogs do not survive long with this condition.
This disease is quite rare. As in cats, the muscles of the heart thicken and become inefficient at pumping blood. The signs of the disease are the signs of congestive heart failure e.g. difficulty breathing, coughing, heart murmurs and exercise intolerance.
The most common reason pets with heart problems come to see veterinarians is because of coughing and breathing problems. These pets tend to breath faster than they should and they tend to be congested. One can have complicated tests performed to evaluate if the medications are doing their job, but monitoring your pet's breathing rate and freedom from congestion at home is just as accurate - perhaps more so. If the medications are working, your pet will breath slower and easier when it is at rest. If you want to confirm your decision about its progress based on its respiration, do so by having your vet run occasional proBNP tests (or Cardio-BNP if your pet is a dog) to confirm their test levels are dropping or holding steady. You can read an article that confirmed that here.