A heart murmur is an abnormal heart sound caused by the vibration of turbulent blood flow. Normally, blood flow is laminar and very quiet. Having a heart murmur is not itself an illness or disease. It is a characterization given to an abnormal sound heard upon auscultation over the region of the heart.
How Heart Murmurs Affect Cats
Cats of any age, breed or gender can be born with or later develop heart murmurs. Many affected cats show no outward signs of having heart murmurs. In fact, most murmurs are detected incidentally during routine veterinary check-ups. When heart murmurs do accompany clinical signs, generally there is something more serious going on with the animal's heart and the murmur is a consequence of – not a cause of - that underlying condition. The signs are nonspecific and depend upon the cause of the heart disease. Some cats will become intolerant to activity or just generally "slow down." They may pant while resting (open-mouth breathing is not normal in healthy cats) and have difficulty breathing. Their mucous membranes may become pale. The cat may cough and appear "pot-bellied" from fluid retention. Heart disease can cause a myriad of other symptoms in cats as well. In some cases, heart problems (possibly suggested by heart murmurs) can be associated with fainting spells or other periods of sudden collapse. This can happen when oxygen is not distributed properly to body tissues through normal blood circulation. If your cat's gums become pale or even approach blue in color, be suspicious of inadequate oxygen supply and get your pet to the vet.
This is cause for immediate concern.
Kittens frequently have "benign" heart murmurs (also termed innocent, functional or physiologic murmurs) which should disappear by 4 to 6 months of age. These are produced because the strong young heart is beating in close proximity to the kitten's chest wall, and therefore the turbulence produced from blood flowing through the heart and large adjacent vessels can be especially prominent. These murmurs frequently are identified at the first kitty check up, and may vary in intensity depending on the animal's health and physical state. Follow-up veterinary examinations will track the murmur as the kitten matures.
Causes of Feline Heart Murmurs
Heart murmurs can be congenital (existing at birth) or acquired and can be caused by many different structural heart defects as well as by a number of infectious and other processes. Any of the heart valves (mitral, tricuspid, pulmonic, aortic) can be affected by endocardiosis, endocarditis, valvular stenosis or dysplasia, with characteristic heart sounds accompanying each type of disorder.
Endocardiosis is a common cause of cardiac disease and is characterized by chronic fibrosis and thickening of the free valve edges, causing anything from minor leakage to severe malfunction.
Endocarditis is an inflammatory change of the tissues lining the heart chambers and valves.
Stenosis is a narrowing or constriction of a body passageway that causes increased turbulence at the affected area. Pulmonic stenosis is a narrowing of the outflow area of the pulmonary artery at the exit from the right ventricle of the heart. The murmur reflects the abnormal turbulence that results where the outgoing blood meets resistance. Aortoic stenosis is a similar narrowing but occurs in the aorta outflow area, and the murmur develops for the same reason.
Dysplasia simply means an abnormality of development, such as some alteration in size, shape, organization or structure. Mitral valve dysplasia is one of the more common cat conditions. This defect results in a leaky mitral valve, and the murmur results from the turbulence of blood reflux.
Other causes of feline murmurs include, but are not limited to:
Atrial and ventricular septal defects - basically, a hole or tear of the interior wall separating the heart chambers. If the hole is very large, murmurs may actually be absent because of decreased turbulence.
Patent ductus arteriosus - a failure to close of an important duct in the fetal heart that will produce shunting of blood in the heart when it remains open after birth. If shunting occurs from the right to the left, murmurs are usually absent. However, in the usual left-to-right side PDA shunt, murmurs can be heard.
Cardiomyopathy - primary disease of the heart muscle, with several distinct forms in cats.
Feline heartworm infection
Tetralogy of Fallot - a complex congenital heart defect that combines four distinct structural anomalies of the heart and emerging arteries.
Characteristic murmurs usually accompany each of these conditions and can be detected by skilled veterinarians through auscultation with their stethoscope.
Preventing Heart Murmurs in Cats
Murmurs are a clinical finding that cannot be "prevented" or even "treated" in the normal sense of those terms. The underlying cause of the murmur must be found. Many heart murmurs will never require medical or surgical management, even if they are very pronounced. Minor murmurs can often be managed with exercise and/or dietary change. Surgical procedures may be available for cats with more serious heart conditions causing their murmurs, although presently surgery is more commonly done in dogs.
If your veterinarian detects a heart murmur in your cat, she will likely recommend advanced diagnostics through use of thoracic radiographs, electrocardiography and/or echocardiography. You may be referred to a specialized veterinary cardiology to perform all or some of this testing. The prognosis for cats with heart murmurs depends almost entirely on the nature and severity of the underlying cause.
Remember, a heart murmur does not necessarily mean that the heart is in failure or otherwise diseased. Heart murmurs generally cannot be "cured," because they are not a disease or illness per se, but their effects may be manageable with medication, exercise and dietary change.
Heart murmurs in cats are diagnosed through a physical examination using a stethoscope, grading the heart murmur based on severity, and identifying what type of heart murmur is occurring based on the heart's sound. An electrocardiogram may help to distinguish the grade and type of heart murmur, and complete blood tests and ultrasound examinations can be used to determine why the heart murmur is occurring.
Types of Heart Murmurs in Cats
There are many different types of heart murmurs, and they are distinguished by their specific sounds that occur on an up or down beat and by their intensity. In many cases, it is difficult to determine exactly what the heart is doing by sound alone, and an echocardiogram (ECG) is often used to get a view of the heart's patterns.
Heart murmurs can be caused by a variety of conditions, and blood tests and ultrasound examinations are often used to determine if a treatable medical condition is causing the murmur, or if the murmur is caused by a physical defect in the heart or an inherited genetic condition.
Grading the Severity of Heart Murmurs in Cats
Heart murmurs are diagnosed based on grades one through six.
A grade one heart murmur is the least severe and it can barely be heard.
A grade two heart murmur is a faint murmur that occurs only in a specific area of the heart.
A grade three heart murmur can be heard immediately once an examination with a stethoscope begins and the sound is widely projected.
A grade four heart murmur can also be immediately heard during an examination and it is accompanied by a vibration known as a thrill
A grade five heart murmur is the loudest murmur
A grade six heart murmur can still be heard when the stethoscope has just been removed from the chest wall
Treating feline heart murmurs is not a realistic or viable option, because heart murmurs are not a disease or illness but rather are simply abnormal heart sounds caused by turbulent blood flow. To "treat" the heart condition, the veterinarian must identify why the murmur exists. Once the cause of the murmur is identified, a treatment program can be formulated.
Treating Heart Murmurs in Cats
Heart murmurs can be congenital (the animal is born with them) or acquired, and the prognosis ranges from excellent to grave, depending on the underlying cause. Available treatment options will vary depending upon the severity of the underlying condition. Many feline heart murmurs do not require "treatment" at all, even if the murmur is very pronounced. Minor heart murmurs can often be addressed by dietary and lifestyle changes without more.
The most common causes of heart murmurs in companion cats are hyperthyroidism and cardiomyopathy. Hyperthyroidism often can be treated or managed through surgery and/or medical regimens. Feline cardiomyopathy often is manageable as well with a combination of drugs and supportive care that will reduce the heart's workload, increase the elasticity of the heart muscle and improve the heart's overall efficiency. Feline heart murmurs caused by anatomical abnormalities may be surgically correctable. Many pet owners are unable or unwilling to proceed with these specialized surgeries, but interested cat fanciers should explore all treatment and management options with their treating veterinarians. Heart murmurs in cats can also be caused by severe anemia from internal or external parasite infestation. Appropriate flea and tick preventative protocols and deworming regimens can be discussed with your veterinarian. Nutritional supplements can also help resolve the anemia and corresponding murmurs in some cases.
Cats with murmurs reflecting underlying heart disease should be kept in a warm, calm, soothing household environment where they can minimize their activity level and rest and relax as needed. In households with young children and other pets, the adults will need to carefully manage their cat's special needs and requirements for rest.