A heart murmur in dogs and cats is generated by turbulent flow of blood through the heart chambers. Doc Martin is trained cardiology, the branch of veterinary internal medicine that deals with diseases and abnormalities of the heart.
Causes of Heart Murmur in Dogs and Cats
Heart murmurs can be normal or pathologic.
- Normal, or innocent heart murmur is physiologic, that is just normal blood flowing through the heart. They need to be investigated to rule our pathology.
- Pathologic murmur are caused by disease. They can be caused by a anatomic abnormality problem within the heart (i.e., cardiac disease), or can be due to a problem outside of the heart (extracardiac) not caused by disease. An example of a anatomic abnormality is a VSD (see image) or ventricular septal defect (hole) that allows blood to flow through creating a sound, “murmur”.
What is a heart murmur?
Basically a heart murmur is an abnormal heart sound heard with a stethoscope. When considering the typical heart beat, it is often described as a “lub-dub” which are the two normal heart sounds in sequence. The first heart sound (S1) and second heart sound (S2) occur in sequence with each heartbeat. These are the first heart sound (S1) is due to the closure of the valves between the atrium and ventricle. The second heart sound (S2) is produced by the closing of the valves leaving the heart.
During a murmur, a “swish-dub” or “lub-swish” is heard. They are usually ranked on a scale of 1-6 with 1 being the softest and 6 being the loudest. The loudness of the murmur does not necessarily correlate with the severity of any underlying disease (e.g. some 2/6 are actually much sicker than some 5/6 murmur patients). Actually, in order for them to be a 5 or 6, they have to be able to be felt when one’s hand is pressed to the side of the chest (“palpable thrill”). Some murmurs are during the first beat (systolic) and some are during the second beat (diastolic). 
Some occur during the entire heart beat cycle without a break (continuous)!
What causes the murmur sound?
In essence it is turbulence of the blood. The blood is swirling or moving in the wrong direction or at speeds higher than it was intended to. You might liken the sound to that made when you vigorously stir a liquid or when you put your finger over the end of a garden hose while it is running at high speed. The stirring or obstruction to flow causes the fluid to move faster which then makes a sound.
What can make the blood swirl or move wrong?
Many things can do this. If the blood is too thin (as in anemia), or if there is an alteration of flow through the valves (faulty valve, or a stiff valve), redirection of blood through an opening or connection that is not supposed to be there (septal defects or Patent Ductus Arteriosis (PDA)), alteration in the timing or rhythm of the heart beat (arrhythmia), or a problem in many other organ systems that secondarily effect any of the aforementioned, a murmur may result. There are some congenital (from birth) defects such as PDA and septal defects that can be very significant diseases and can show murmurs in even the youngest of animals.
Is a heart murmur fatal?
In and of itself, no a heart murmur is not fatal. However, it is something that needs to be addressed and the source found because it is a sign of many different diseases that if caught early enough can be treated. There is also a condition often referred to as a benign or incidental or innocent murmur. These are murmurs that can be heard but for which absolutely no disease or pathology can be found.
What tests are performed to check a heart murmur?
Often there is a combination of tests performed to try to determine the source of the murmur. Blood work, urinalysis, ECG (EKG), chest x-rays, blood pressure monitoring and ultrasound are the main tests that are used. They need to be done together to be sure the source and severity of the problem can be found. There is no one test that tells all that can be told about the heart.
- Blood work and urinalysis check the main organ systems which often control thickness of the blood, blood pressure, protein levels, and electrolytes. It can also indicate infection which can cause secondary heart disease. Deviation in any of these can affect the heart. There is also a test that can indicate excessive stretching of the heart muscle.
- ECG (EKG) helps analyze the rhythm of the heart and its natural pacemaker.
- Chest x-rays indicate size, shape, and position of the heart. They can also tell us if there is fluid backing up into the lungs which is often a sign of heart disease.
- Ultrasound can help visualize thickness of the heart wall, valve function, blood flow through the heart, effectiveness and distance of heart muscle contraction to name a few. We most often do ultrasound after all of the other tests and/or if our treatment is not working as we expect. This test we usually schedule in clinic with a mobile service or refer out to a specialist locally.
What is the prognosis for my pet with a murmur?
That question is difficult to answer without knowing the cause of the murmur. A vast majority of pets with murmurs have conditions for which there are many options for treatment that continue to provide increased quantity of high quality lives. This question is best addressed case by case with your veterinarian.
What are some basic take-home points about heart murmurs?
- Heart murmurs are not normal.
- Heart murmurs often indicate a significant underlying problem and should not be ignored.
- Heart murmurs do not tend to “go away on their own.”
- The murmur is an abnormal sound caused by abnormal blood flow for a variety of reasons.
- The diseases they can indicate are often treatable.
- The murmur is not life threatening in and of itself, but it often warns of diseases that can be fatal if left untreated.
- Heart murmurs can occur at any age.
If you suspect a heart murmur in your pet dog or cat and would like further information, from the Plantation Pet Health Services, please call 972-731-0001 to schedule an appointment or complete an Online Appointment Request.
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