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Heart Murmurs in Cats

What is a Heart Murmur?

Heart murmurs can be an incidental finding auscultated by your vet during a routine check when listening to your cat’s heart. Murmurs are caused by the high-velocity turbulent flow of blood as it travels through the heart. This happens when the blood flows backward, opposite the usual pathway of forward movement.

Classification of Heart Murmurs

Heart murmurs are always considered abnormal at the moment of a checkup; however, having a heart murmur doesn’t necessarily mean that your cat has a heart condition. The presence of a murmur can be linked to non-cardiac conditions like fever, hyperthyroidism, lactation, or anaemia.

On the other hand, not finding a heart murmur at the moment of the physical examination doesn’t rule out the presence of heart disease, as some cardiac diseases do not necessarily produce audible heart murmurs.

Causes of Heart Murmur

  • Physiologic (“innocent”) murmurs are present in the absence of cardiac disease: fever, kittens, lactating cats, anaemia, stress.
  • Structural cardiac disease

Common Heart Diseases in Cats

Hypertrophic cardiomyopathy (HCM) is the most common heart condition diagnosed in cats. While the cause of this disease hasn’t been identified yet, it has been suggested a possible genetic predisposition, being the main breeds affected: Maine Coon, Ragdoll, British Shorthair, Sphynx, and Persian cats. This condition consists of the thickening of the heart’s wall, making it harder for the heart to pump blood efficiently.

Dilated Cardiomyopathy (DCM) is a condition where the heart chambers enlarge, and as a result, the heart muscle gets thinner, leading to poor contraction and pumping of blood. This disease is becoming less common among cats due to an improvement in feline commercial diets.

Is There Any Breed Predisposition to Heart Disease?

Yes! It has been proven that some breeds are genetically predisposed to certain heart diseases.

  • Maine Coon: About 33% of their population are predisposed to HCM, which can affect them even at a young age (before four years old)
  • American and British Shorthair: HCM
  • Persian Cats: high incidence of HCM
  • Siamese Cats: patent ductus arteriosus (PDA) and DCM. The ductus arteriosus detours the blood away from the lungs during prenatal life as they are not used while in the uterus. This duct normally closes at birth; however, If the ductus persists open after birth, it will severely limit the amount of blood that reaches the lungs.

Grading Heart Murmurs

Heart murmurs are graded on a scale from I to VI depending on how loud they are at the moment of the auscultation, with grade I being the softest and grade VI the loudest. The volume of the murmur can be affected by different factors, such as noisy environments, growling, hissing, purring, and/ or obesity. It is important to understand that the murmur volume doesn’t always reflect disease or severity. Also, murmurs in cats can vary in intensity with stress or changes in heart rate.

What Should I Do if My Cat Has a Heart Murmur?

Differentiation of heart murmur causes is not possible by auscultation alone. When the vet first detects a heart murmur, they will look at the whole picture, trying to find other signs that might indicate an underlying cause for the murmur. Depending on the findings, your vet might suggest further testing such as blood tests, chest X-rays, or an echocardiogram (ultrasound of the heart). So far, an echocardiogram is considered the only way to identify whether a heart murmur is caused by cardiac disease. This is a non-invasive procedure, usually performed without the need for sedation.

While some heart murmurs can be considered “innocent” or transient, they can also be an indicator of a more serious disease. The good news is that heart murmurs can be easily detected during a general checkup with your veterinarian. Thus, once your vet has heard a heart murmur in consultation, further testing might be recommended to find out the cause of the murmur and eventually start treatment, if indicated.