A heart murmur in dogs is an extra sound that a veterinarian can detect during a physical examination, often described as a “whooshing” noise in addition to the normal heartbeat. These murmurs can range from very faint to quite loud, sometimes even palpable when a hand is placed on the dog’s chest. Graded on a scale of 1 to 5, with 1 being the mildest and 5 the loudest, heart murmurs can potentially lead to congestive heart failure. However, the progression largely depends on the dog’s overall heart efficiency and the owner’s approach to diagnosis and management. Regular wellness exams are crucial, as most heart murmurs are identified during these routine check-ups, underscoring the importance of annual veterinary appointments. “Early diagnosis helps us intervene while there’s still something we can do about it, whether it’s a puppy with a congenital problem, or an older dog with a new murmur,” states Dr. Erin Corrigan, D.V.M. ’98, medical director at VCA Fairmount Animal Hospital.
A normal resting respiratory rate for a dog is between 15 to 30 breaths per minute. If a relaxed or sleeping dog exhibits a respiratory rate exceeding 35 breaths per minute, it can signify underlying heart issues and warrants an immediate veterinary visit. You can accurately assess your dog’s respiratory rate by observing their chest movements for 15 seconds, counting the number of rises, and multiplying by four. It’s vital to begin monitoring this early, as visible symptoms of heart problems—such as difficulty breathing, rapid breathing, coughing, weakness, lethargy, exercise intolerance, and collapsing—often indicate that heart disease has already progressed significantly.
Types of Heart Murmurs in Dogs
Heart murmurs in dogs can be broadly categorized into two main types:
Congenital murmurs are present from birth, typically resulting from structural heart defects. Fortunately, many murmurs detected in young puppies are benign, often referred to as “innocent” or “physiologic” murmurs. These softer murmurs are usually outgrown by approximately six months of age.
Acquired murmurs develop later in a dog’s life and are commonly associated with heart valve abnormalities or cardiac muscle disease. Many dogs diagnosed with acquired valvular disease may never progress to congestive heart failure with appropriate care. These murmurs often affect one of the heart valves, with myxomatous mitral valve degeneration being a frequent cause. This progressive degeneration of the mitral valve, where the cause is not fully understood, has a known genetic link in breeds like Cavalier King Charles Spaniels. Larger breeds may also develop murmurs related to cardiomyopathy, a condition affecting the cardiac muscle.
The mitral valve, situated between the left atrium and left ventricle, plays a critical role in directing oxygenated blood from the lungs to the left ventricle, which then pumps it to the rest of the body. Its function is to close after each heartbeat, preventing blood from flowing back into the left atrium. Degeneration of the mitral valve causes it to become irregular and unable to close completely, allowing blood to regurgitate into the left atrium. Over time, this increased blood volume causes the left atrium to stretch and enlarge, leading to reduced heart efficiency and increased workload. Eventually, fluid can back up into the lungs, resulting in congestive heart failure, which necessitates lifelong cardiac medication.
The Importance of Monitoring and Management
If your veterinarian detects a heart murmur, they will likely recommend an echocardiogram to confirm the diagnosis and assess baseline cardiac function. Annual echocardiograms are an excellent way to track the progression of the condition. This non-invasive procedure, typically performed without sedation, is a crucial diagnostic tool for managing your dog’s heart health.
A simple blood test, known as pro-BNP, can also aid in monitoring. Levels of this peptide increase when the cardiac muscle is stretched or stressed. It might take several years for a dog’s heart disease to progress to the stage requiring medication, and some dogs may never need it. In the interim, maintaining a healthy weight is paramount for supporting long-term cardiac health. Obesity exacerbates breathing difficulties, placing additional strain on the heart, and can limit exercise, which is beneficial for cardiovascular function.
Specialized veterinary diets, such as Purina’s Pro Plan Veterinary Diet CardioCare, have shown promise in slowing the progression of early-stage cardiac disease. Hill’s Prescription Diet Heart Care h/d and Royal Canin Veterinary Diet Early Cardiac are other effective options. These diets are formulated with restricted sodium to help prevent fluid accumulation and support healthy blood pressure, crucial for cardiac patients. They also contain antioxidants, anti-inflammatories, and other nutrients that promote cardiac function.
If your dog is diagnosed with a heart murmur, schedule regular follow-up appointments to monitor its progression. Supporting your dog’s weight management through appropriate diet and exercise, and potentially using a prescription cardiac diet, can significantly impact their quality of life and longevity. Proactive cardiac management can be the key factor in preventing congestive heart failure and ensuring your dog lives a longer, healthier life.
Murmurs in Puppies: Usually Not a Cause for Alarm
The majority of heart murmurs detected in puppies are benign, meaning they pose no harm. These are typically soft “physiologic” murmurs that most puppies outgrow by six months of age. If a puppy does not outgrow their murmur, an echocardiogram is recommended to identify the cause, assess cardiac status, and determine the prognosis. This is important regardless of whether the puppy is intended for breeding.
For breeding dogs, an echocardiogram helps determine ethical breeding suitability. In dogs undergoing spay or neuter procedures, it provides the veterinary surgeon with vital information regarding anesthesia risks. The long-term outlook for puppies with congenital heart defects varies; many will live normal lifespans, while others may be candidates for surgical intervention.
This article was reprinted with permission from the Cornell University College of Veterinary Medicine’s DogWatch newsletter.