All kinds of health conditions can affect our dogs, from treatment-defying cancer to patience-testing dermatitis to nobody-to-blame-but-myself parasites. But somehow, when the heart is involved, it strikes us to our core. So, we thought we’d take a look at one of the more troubling potential signs of heart problems – murmurs. It’s one of those words that make dog lovers draw in a quick breath and immediately start imagining the worst.

While murmurs can indicate trouble, they don’t in every case. And, even when they do, it’s always better to be informed and get an early diagnosis than to wait and regret it later. Just remember that murmurs aren’t a disease in themselves, but rather a potential sign of disease.

A stethoscope, in the hands of a capable veterinarian, can detect even the slightest of heart murmurs. Photo © Can Stock Photo.

“A heart murmur is a clinical finding, not a disease,” says Rebecca L. Stepien, D.V.M., M.S., a clinical professor of cardiology at the University of Wisconsin-Madison School of Veterinary Medicine and a diplomate of the American College of Veterinary Internal Medicine. “It’s sort of like a swollen joint. We have to find out why it’s swollen.

“So when a murmur is detected, we look for the reason for the murmur. That reason may be a congenital malformation of the heart that causes turbulent blood flow, or it may be due to acquired changes in one or more valves due to aging or infection, or in some cases, can be found in normal animals – especially canine athletes,” Stepien says.

Before we get into the causes of murmurs, let’s do a quick tutorial on the anatomy of the heart, which we all know looks nothing like those symmetrical, bright red ones we saw plastered pretty much everywhere last month.

The structure of a dog’s heart is the same as a human’s. Photo © Can Stock Photo. //Link “Can Stock Photo” to

The Heart’s True Shape
The bulk of the canine heart – and the human one for that matter – is its four chambers. The two ventricles on the left and right run somewhat vertically from the bottom, divided by the ventricular septum (kind of like the septum in our noses). Above the left ventricle is the left atrium, a smaller chamber, and above the right, the right atrium. They are surrounded by connective and muscle tissue.

Four valves are key to the heart’s function: the mitral valve, tricuspid valve, aortic valve and pulmonic valve. Blood flows into the heart through the tricuspid valve on the right and the mitral valve on the left. It is pushed out of the heart through the pulmonic valve on the right and the aortic valve on the left. The valves, within the four chambers of the heart, “are critical to the proper flow of blood through the heart,” according to the University of Southern California Keck School of Medicine. “All of the valves, when functioning normally, act as one-way valves, allowing blood to flow either from one chamber to another, or allowing blood to flow out of the heart, in only one direction. The valves control the flow of blood through the heart by opening and closing during the contractions of the heart. The opening and closing functions of the valves are controlled by pressure differences generated within the heart, as well as some muscles located within the heart.”

Numerous arteries feed off the heart, but the main ones are the aorta and the pulmonary artery. The pulmonary takes blood that’s been drained of oxygen to the lungs via three routes. The aorta sends re-oxygenated blood to the body via four routes. With each pump of the heart, blood moves out into the body.

So, based on the heart’s anatomy, it’s easy to see how important valve function is to heart function.

A complete veterinary examination always includes listening to the heart for a normal “lub-dub” sound. Photo © Can Stock Photo.

Not a ‘Lub-Dub’
When listening to your healthy dog’s heart, your veterinarian will hear a “lub-dub” sound, Stepien says. During what is known as “auscultation,” she will also check the rhythm and heart rate. Any muffling of the sound or a stronger “lub” than “dub” or vice versa may indicate a problem.

The sounds the heart makes are “generated when blood within the heart hits a closed valve during contraction or relaxation,” Stepien explains. “If a valve doesn’t close completely, some blood may flow backwards during contraction or relaxation. The backward flow of blood creates the sound of the murmur.”

If your veterinarian here’s a murmur, she will grade it based on the following:

  • Grade I: The lowest intensity murmur that can be detected only after listening for several minutes.
  • Grade II: A soft murmur that can be detected immediately, but is confined to a small area.
  • Grade III: A moderately intense murmur, detected immediately and not confined to a small area.­
  • Grade IV: A loud murmur, normally detected on both sides of the chest that does not include the  vibration known as a “precordial thrill.”
  • Grade V: A very loud murmur that includes a palpable precordial thrill.
  • Grade VI: An extremely loud murmur with a palpable thrill that can be heard without the stethoscope touching the dog’s chest.

“Whether a loud or soft murmur indicates worse abnormality is very dependent on the disease,” Stepien says. “A loud murmur generally indicates more severe abnormality, with the exception of a congenital ventricular septal defect,” often called a “hole in the heart.”

Behind the Murmur
Five conditions are the major causes of heart murmurs.

In tricuspid regurgitation, a valve doesn’t close correctly. It can be acquired or congenital, Stepien says. If heart failure or arrhythmias – irregular heart rhythms – result from the condition, they may be treated with anti-arrhythmic medications like beta-blockers or calcium channel blockers. “The prognosis for tricuspid regurgitation depends on the severity of the problem. Dogs that have clinical signs due to tricuspid regurgitation – like fluid accumulation in the abdomen (ascites) or abnormal heart rhythms – may have a good quality of life with medications to treat these problems.”

As mentioned above, a ventricular septal defect is a hole or multiple holes in the wall that runs between the ventricles. Dogs are born with this condition, rather than developing it. The prognosis depends on the size of the hole or holes, Stepien says. With larger defects, heart failure or arrhythmias may develop, and the dog will be treated for those. Dogs with small ventricular septal defects may have a normal life span after diagnosis, with no limitations on activity or lifestyle changes.

Myxomatous mitral valve disease is an acquired disease that causes the mitral valve between the upper and lower chambers on the left side of the heart not to close properly, and can lead to mitral regurgitation, also called mitral insufficiency, Stepien says. As with the previous conditions, any heart failure or arrhythmias resulting are treated, and the prognosis depends on their severity and whether there are other complications, such as development of pulmonary hypertension – high blood pressure in the pulmonary arteries, Stepien says. After diagnosis, dogs without clinical signs may live for three to five years before signs of heart disease, such as fatigue or cough, develop. Dogs without clinical signs do not need to have any limitations on exercise, but maintaining a healthy weight and body condition is encouraged. Mitral regurgitation may also occur with congenital malformations of the mitral valve, known as “mitral dysplasia,” she says. A dog with this kind of malformation may have a normal life span without any activity limitations if the mitral regurgitation is not severe.

A narrowing of the aortic or pulmonary valves, known as “stenosis,” is usually congenital, Stepien says. Because of the narrowed valves, the heart works harder than it normally would. “Pulmonic stenosis may be treated with balloon valvuloplasty performed during cardiac catheterization,” she explains, and “prognosis for relief of signs is often good.” In this procedure, a small balloon is inserted through an artery into the valve, then filled with just enough air to widen the valve. While aortic stenosis is “sometimes” treated with valvuloplasty, results are “variable,” Stepien says. “Severe aortic stenosis often is associated with life-threatening arrhythmias,” she adds.

Complications of either type of stenosis may include inability to exercise, fainting and irregular heart rhythms, and will affect the prognosis.

A dog with pulmonic stenosis that undergoes valvuloplasty can have a normal life span if the procedure is successful, and may resume its regular routine after recovery from the procedure. Dogs with aortic stenosis have variable prognoses based on the severity of the problem. Dogs with mild aortic stenosis may live a normal life span with no restrictions, but dogs with severe cases may live only three to five years.

As with the other conditions, resultant heart failure and arrhythmias are treated with medication.

The congenital defect patent ductus arteriosus results when the blood vessel that keeps most blood out of puppies’ lungs in utero doesn’t close after birth. A portion of the blood leaving the heart through the aorta continues to flow between the aorta and pulmonary arteries, rather than all of it flowing through the aorta and the rest of the body. The vessel can be closed during a cardiac catheterization with an Amplatzer vascular plug, which essentially blocks the vessel by causing a blood clot to form, or with an intravascular coil that has a similar effect, Stepien explains. Surgery to close the vessel is another option. “In both cases, the prognosis is good for full recovery,” she says. “If left untreated, most dogs with PDA will have congestive heart failure or other complications within one to three years. Heart failure and arrhythmias are treated medically, if present, prior to closure of the PDA.”

Puppies whose PDA is corrected should have normal life spans for their breed and usually need no special care.

No magic bullet for preventing heart disease exists, but healthy body weight, exercise and a high quality diet are a good start, according to Rebecca L. Stepien, D.V.M., of the University of Wisconsin-Madison School of Veterinary Medicine. Photo © Can Stock Photo.

Building Healthier Hearts
Healthy body weight, exercise and a high quality diet are all commonsense methods to assure a dog’s overall good health, according to Stepien. She adds that no evidence exists that “CoQ10 has any effect on dog’s heart health. Similarly, although most veterinarians recognize that dental health is important and therefore recommend good dental care throughout a dog’s life, there is no evidence that dental disease causes heart disease.”

A test – NT-proBNP – is available to distinguish heart failure from respiratory causes of the respiratory signs associated with heart failure. “We generally do not recommend this test for dogs without any signs of the disease,” Stepien says, “except for Doberman Pinschers, in which the test may be helpful to detect dilated cardiomyopathy before clinical abnormalities are noticed.” The test, she adds, is “useful as one of several tests to detect early, preclinical heart disease in Doberman Pinschers. This test should not be used for random screening of healthy dogs.”

However, there’s no magic bullet for preventing the diseases that cause heart murmurs.

“Veterinary cardiologists generally recognize that acquired heart disease may be an interaction between a genetic predisposition, aging changes and other unknown factors,” Stepien says. “Therefore, our major recommendation is to take good care of pets’ general health, and keep up with routine veterinary examinations to catch any problems early. At this time, there are no proven methods to ‘prevent’ acquired heart disease in most cases.”

As to breakthroughs in treatments, she says, “The most important changes that have taken place in the last several years involve the clinical testing of heart failure therapy in dogs with acquired heart diseases. Recent clinical trials of heart failure therapy have proven that, with good owner care and good veterinary care, dogs with heart disease and heart failure can have a high quality of life for longer and longer periods of time. Clinical trials are excellent ways of testing new therapies, and in the past few years, several well-done trials have shown which therapies have the most benefit for dogs with heart disease.”

So, if you think your dog’s heart is “murmuring” to you, get it checked out. The sooner you know there’s a problem, the sooner your veterinarian or veterinary cardiologist can start treating it.