What is a heart murmur?
A heart murmur is an abnormal heart sound, usually heard by listening to the heart with a stethoscope.
What causes a heart murmur?
A heart murmur is caused by turbulent blood flow within the heart. Sometimes a murmur is determined to be 'innocent' or 'physiologic', while other times the murmur is determined to be pathologic or caused by disease. Pathologic heart murmurs can be caused by a structural problem within the heart (i.e., cardiac disease), or can be due to a problem that is 'extracardiac' (i.e., not caused by heart disease).
Do all murmurs sound the same?
No. The loudness of a murmur reflects the amount of turbulence that is present in the heart. However, the loudness of a heart murmur does not always correlate directly with the severity of disease.
Murmurs are graded by their intensity, usually on a scale of I-VI. A Grade I murmur is very soft or quiet, may only be heard intermittently, and is usually only heard in one location on the chest, while a Grade VI murmur is very loud, heard everywhere that the heart can be heard, and can be felt when a person places their hand on the chest in the area of the heart (in cardiac terminology, this is called a 'thrill').
Murmurs are also characterized by the time in which they occur during the heart cycle, and by whether they are long or short. Most murmurs are also characterized by their location, or where they are the loudest.
The majority of murmurs in the dog occur during systole, the phase of the heart cycle when the heart is contracting to pump blood out.
The specific characteristics of the murmur, along with any symptoms that your dog might be showing, will help your veterinarian to determine what is causing the murmur.
What is an innocent, physiologic or Puppy heart murmur?
An innocent or physiologic or Puppy heart murmur is a heart murmur that has no impact on the dog's health.
It is very common for young puppies, especially large breed puppies, to develop an innocent heart murmur while they are growing rapidly. The murmur may first appear at 6-8 weeks of age, and a puppy with an innocent heart murmur will usually outgrow it by about 4-5 months of age. This type of murmur is benign.
In general, a physiologic or innocent heart murmur will have a low intensity (usually Grade I-II out of VI), and does not cause any symptoms or clinical signs.
What structural heart problems cause a heart murmur?
The heart is composed of four chambers - the left atrium, the left ventricle, the right atrium, and the right ventricle. Blood flows from the right side of the heart through the pulmonary artery to the lungs where it is oxygenated, and then the oxygenated blood goes through the left side of the heart and into the aorta, where it is pumped to the rest of the body. Between each of the chambers and main blood vessels there is a valve that functions to prevent blood flowing back into the chamber as the heart pumps.
With structural heart disease, there is some sort of abnormal structure or defect that is disturbing the flow of blood, creating turbulence. The abnormality in the heart may be a leaky heart valve, a thickening or narrowing of a valve or large blood vessel, or an abnormal hole between the heart chambers or between two arteries that are not normally connected.
Structural heart problems may be congenital (the dog is born with a defective heart) or acquired (a structural heart problem develops later in life). Some of the congenital heart diseases in dogs are hereditary in certain breeds of dogs, and include diseases such as 'sub-aortic stenosis', 'pulmonic stenosis', and 'patent ductus arteriosis'. Other congenital heart diseases are not as well documented as being hereditary, including 'ventricular septal defects', 'atrial septal defects' and 'Tetralogy of Fallot'. The most common cause of an acquired heart murmur in the dog is 'mitral insufficiency' (also called 'mitral regurgitation'), a condition in which the mitral valve becomes thickened and begins leaking (see our handout 'Mitral Valve Disease in Dogs') - mitral insufficiency tends to be more common in small breed dogs. Other causes of an acquired heart murmur in older dogs include bacterial endocarditis, caused by a bacterial infection that localizes on a heart valve and dilated cardiomyopathy (see our handouts 'Endocarditis in Dogs' and 'Dilated Cardiomyopathy in Dogs').
What extracardiac problems cause a heart murmur?
Some extracardiac problems can cause what is called a 'functional heart murmur'. A functional heart murmur may be due to anemia (low levels of red blood cells), hypoproteinemia (low protein levels in the blood), fever or infection, or by conditions such as pregnancy, obesity or emaciation. With anemia or hypoproteinemia, the blood is too 'watery' so turbulence is created as it flows through the valves.
With young puppies, anemia and/or hypoproteinemia can be caused by a heavy infestation of parasites such as intestinal worms, blood parasites, fleas or ticks. Adult dogs may become anemic because of blood loss or may have a serious underlying disorder.
How is a heart murmur detected?
In most cases, a heart murmur is detected when your veterinarian auscultates or examines your dog's heart with a stethoscope.
How do we find out if a murmur is due to a significant problem?
Most murmurs are detected with a stethoscope during a routine veterinary examination. If your veterinarian detects a heart murmur, you will be asked a series of questions about your dog's health and then your veterinarian will assess your dog's general physical condition to determine whether or not there are any symptoms or clinical signs that indicate the need for further diagnostic testing.
If your pet is still a young puppy and the murmur is of low intensity, your veterinarian may recommend a re-examination in a few weeks time to track whether the murmur has decreased in intensity or disappeared, indicating that it was likely an innocent murmur. Similarly, if your adult dog appears to be extremely stressed at the time of a routine health examination and the murmur is of low intensity, your veterinarian may recommend a re-evaluation at a later time when the dog is calmer. In some cases, if a dog is extremely excited or is panting heavily, it can be difficult to determine if abnormal sounds are being caused by a heart murmur or are just related to the elevated heart rate or panting.
A dog with a heart murmur that is caused by a structural heart disease or an extracardiac problem will generally have some sort of symptoms or clinical signs that can be attributed to the disease. The most common symptoms that are observed with a dog that has a clinically significant heart murmur are poor appetite, weight loss (or stunted growth in a kitten), breathing problems, often occurring in the middle of the night or after the dog has been lying down for a period of time, poor exercise tolerance, collapse or fainting spells, pale gums, and/or coughing.
During a physical examination, if your veterinarian detects an abnormal rhythm to the heartbeat, or finds that your dog has weak pulses or irregular pulses, it will be more likely that the murmur is caused by an underlying problem. If your veterinarian determines or suspects that the heart murmur is caused by structural heart disease or an extracardiac problem, further diagnostic testing will be recommended. In the majority of these cases, further diagnostic testing should be performed immediately so that any treatment can be started as soon as possible.
What other tests may be recommended?
Depending on what other clinical signs are present in your dog, your veterinarian will usually recommend x-rays, an electrocardiogram, or an ultrasound examination of the heart (called an echocardiogram). If your veterinarian suspects that the heart murmur is secondary to another disease, blood tests or other extensive tests might be recommended.
An echocardiogram that includes a Doppler examination is the most useful test to determine the location of a heart murmur. With an echocardiogram, the heart is imaged while it is beating, allowing the examiner to evaluate the heart's size and movement. A Doppler examination is a specialized type of echocardiogram in which the speed and direction of blood flow can be measured across the heart valves and in the heart chambers. The Doppler examination will usually pinpoint the location of the turbulence that is causing the murmur.
How is a heart murmur treated?
Heart murmurs are simply abnormal heart sounds caused by turbulent blood flow, and treatment depends upon the underlying cause of the heart murmur or the turbulent blood flow. Physiologic heart murmurs do not require any treatment; however, regular monitoring of a dog that has evidence of a physiologic murmur is advised to ensure that no other problems develop. If the heart murmur is caused by an underlying problem, the treatment plan will be based on the diagnosis, and may include a combination of specialized diets, medications and supportive care. Some congenital heart defects can be surgically corrected - these include pulmonic stenosis and patent ductus arteriosus. Your veterinarian will be the best person to advise you on the appropriate course of action to meet your dog's unique needs.
What is the prognosis?
The prognosis ranges from excellent to grave, depending on the cause of the murmur. If the murmur is physiologic, no treatment is required and the prognosis is generally good to excellent. If the murmur is caused by extracardiac disease or a functional problem that can be treated, the murmur may resolve over time. The long-term prognosis for a dog with a murmur caused by congenital heart disease is extremely variable, depending on the specific type of defect that is present; if the defect can be surgically corrected the prognosis is very good.
A dog with mitral insufficiency can usually be managed with long-term medications. The prognosis for a dog with dilated cardiomyopathy varies - if the dog is showing symptoms of heart failure the prognosis will be grave. The prognosis for a dog with bacterial endocarditis will vary with the severity of the infection and the valve that is affected. The need for good dental care, including regular professional dental cleaning under general anesthesia cannot be overemphasized as a means of preventing endocarditis (see our handout "Dental Disease in Dogs").
Since each case is different, your veterinarian will discuss the prognosis and treatment options for your dog, based on the results of diagnostic testing. In all cases, ongoing monitoring and periodic diagnostic testing will be necessary to track the progress of the condition.
Heart disease in companion animals is too often a silent killer. By the time your dog or cat shows the classic signs of heart disease like lethargy, wheezing, croupy coughing (a liquid-sounding cough, as though there's fluid in the lungs) or exercise intolerance, it's very often too late to save your beloved pet. To make matters worse, an enlarged heart can't be detected with a stethoscope. Significant heart disease can be present and undiagnosed by your veterinarian long before your pet shows clinical symptoms of illness. Too many pet owners too often find themselves in this heartbreaking situation.
Two Types of Heart Disease
Both dogs and cats are at risk for heart disease, and both can develop either type:
Heart muscle disease
Cardiomyopathy is the scientific term for an enlarged heart muscle.
Some breeds of dogs are predisposed to the condition, including New Foundlands, Great Danes and Dobermans.
Cardiomyopathy can also be caused by a dietary deficiency. The amino acids taurine and carnitine are critical for normal heart development and performance. If your dog's or cat's diet is lacking in these amino acids, heart muscle damage can result.
Poor valve health can also lead to heart disease. A leaky valve makes your pet's heart work harder, and the harder it works, the bigger it gets. Valve disease leads to congestive heart failure in both dogs and cats.
Heart murmurs (which are usually present when there are valve problems) are ranked on a scale from 1 to 6, where 1 is considered mild and 6 is the worst case.
Leaky valves or heart murmurs are frequently seen in predisposed breeds like the Cavalier King Charles Spaniel. Leaky valves are also found in aging pets and animals with some metabolic conditions like feline hyperthyroidism.
Diagnosing Heart Disease in Your Pet
If your veterinarian suspects a heart problem -- usually by hearing a murmur through a stethoscope, by doing a physical examination, and/or by considering symptoms your dog or cat is experiencing -- diagnostic tests will be required to confirm presence of disease. These tests, usually x-rays, EKG or cardiac ultrasound, can cost several hundred dollars.
For many pet owners who want to be proactive in detecting heart disease in a dog or cat, the expense of these tests is prohibitive. It's a terrible situation to be in. If you've lost a dog or cat to heart disease, you're bound to be fearful it could happen again to another pet. You want to take proactive steps to help your current dearly loved dog or cat avoid the problem, but you can't afford the tests that will tell you whether or not you need to do more to insure the health of your companion animal. It feels as if you have no choice but to wait to see if heart disease sneaks up silently to claim another four-legged member of your family. That is, until now.
A Blood Test for Early Detection of Heart Disease in Pets
This is wonderful news! At long last, veterinary medicine has developed a blood test that can identify which dogs and cats are at greatest risk for heart disease and heart failure. The test is called a proBNP test. BNP = B-type Natriuretic Peptide.
The proBNP is a blood test that measures how much peptide hormone, released by the heart, is in circulation in your pet's body. This hormone is only released when the heart is pushed beyond its capacity. Very early in the disease process, small amounts of the hormone will be released into your dog's or cat's bloodstream, and it's presence is a signal that steps must be taken in order to preserve your pet's heart health. If heart pathology continues to progress, the blood value of the peptide hormone will continue to rise. How to Proactively Protect Your Pet's Heart Health Ask your veterinarian for the proBNP blood test if you're concerned about your pet's heart for any reason. The proBNP blood test can give you peace of mind that your pet has no early signs of heart disease. It can also help you and your veterinarian differentiate between, for example, a respiratory condition like feline asthma and an underlying heart condition. The proBNP is a simple blood test with a fast turn-around time that can provide the information you need to proactively manage your dog's or cat's heart health. You can have the test repeated as often as necessary to chart your progress in meeting your pet's cardiovascular health needs throughout his life.
Make sure you're meeting your pet's CoQ10 requirement . CoQ10 is a naturally occurring coenzyme that young dogs and cats have in plentiful supply. But as she ages, your pet's ability to produce CoQ10 decreases.
I recommend you supplement your pet's amino-acid-rich diet with Coenzyme Q10, especially if you have an animal that is predisposed to cardiovascular disease. Supplying your pet with extra CoQ10 can insure she has the quantity her body needs to maintain a healthy heart muscle. CoQ10 supplements come in two forms: Ubiquinone and Ubiqunol. Ubiquinol is a reduced form of CoQ10 and is the supplement I recommend for my dog and cat patients. A good heart-healthy maintenance dose is:
50 mg per day for cats and small dogs
100 mg per day for medium sized dogs
100 mg twice per day for large dogs