What Causes a Heart Murmur in Cats? A heart murmur is a fairly common finding in cats, and it means that there are extra or unusual sounds coming from the heart. Sometimes this can be due to disease, but often it’s just benign. It’s important to remember that just because your cat has a heart murmur, it doesn’t mean that he is sick or diseased.

Heart murmurs are categorized by their timing. Systolic murmurs occur during the contraction of the heart (systole) when blood pressure is highest; diastolic murmurs happen when the heart relaxes between beats (diastole). So an early systolic ejection murmur happens during ventricular contraction; a late systolic murmur happens during ventricular relaxation. In other words, early systolic murmurs are associated with narrowing or obstruction of a valve, where the blood is being forced through a narrow passage. Late systolic murmurs are usually due to an abnormal opening of a valve.

Diastolic murmurs occur during ventricular relaxation between beats and often indicate stiffening (constriction) of the heart muscles as they’re relaxing. Early diastolic murmurs happen when there’s extra blood flow from either too much pressure in the heart or from regurgitation from an incompetent mitral valve. The Ejection click, S1 can also be heard as a diastolic murmur which occurs due to the regurgitation outflow of blood during left atrial contraction against the closed mitral valve.

Late diastole can indicate problems with collapsing of the left ventricle. This murmur is commonly heard in cats with hypertrophic cardiomyopathy (thickened heart muscle).

Murmurs can also be either systolic or continuous and ejection, which means that they’re only during the time when blood is being ejected from the heart into circulation — early systolic and late systolic murmurs — or they can be continuous throughout both phases, known as holosystolic mummer. Continuous murmurs are usually due to turbulent blood flow such as mitral regurgitation (blood leaking back through a defective mitral valve), patent ductus arteriosus (a persistent communication between the pulmonary artery and the aorta), or patent foramen ovale (a persistent communication between the right and left atrium).

In cats, most murmurs are just innocent findings. In fact, they’re so common that most veterinarians wouldn’t even bother to discuss them with pet owners unless they were present for a long period of time or there’s some other worrisome symptom that goes along with it. However, because heart murmurs can be due to serious disease, a thorough examination of your cat is important if there’s anything suspicious about his behavior, appetite, breathing pattern, etc., especially in young cats under 5 years old.

An exam should include listening to your cat’s heart directly while he’s lying still on his back if possible. Your veterinarian may use a stethoscope, but most cats hiss and/or move when they see the cold metal of a stethoscope approaching which usually makes it difficult to get an accurate reading. The most common instrument used these days is a handheld Doppler device. In addition, your vet will examine your cat’s heart by palpitation (feel) for any abnormalities such as enlargement or swelling.

Electrocardiography (ECG) readings are also often recommended to help evaluate the electrical activity of the heart since some pets can have abnormal cardiac arrhythmias. An echocardiogram (ultrasound exam of the heart) should be performed to examine the structure and function of your cat’s heart more closely.

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