Heart murmurs in cats are often detected during a routine physical exam by listening to the heart with a stethoscope. A disturbance in the blood flow produces a “whooshing” sound or another noise in addition to the heartbeat.
What causes a heart murmur?
A heart murmur is caused by turbulent blood flow within the heart. Some murmurs are considered innocent or phsyiologic. These murmurs, while not considered normal, have no impact on the cat’s health. Common causes of heart murmurs are hyperthyroidism, high blood pressure, a thickening of the heart muscle, or heart disease.
Not all heart murmurs are created equal
Not all heart murmurs sound the same. The loudness of a murmur doesn’t necessarily correlate to the severity of disease. Murmurs are graded by intensity on a scale of I through VI.
- Grade I—barely audible
- Grade II—soft, but easily heard with a stethoscope
- Grade III—intermediate loudness; most murmurs which are related to the mechanics of blood circulation are at least grade III
- Grade IV—loud murmur that radiates widely, often including opposite side of chest
- Grade V—very loud, audible with stethoscope barely touching the chest; the vibration is also strong enough to be felt through the animal’s chest wall
- Grade VI—very loud, audible with stethoscope barely touching the chest; the vibration is also strong enough to be felt through the animal’s chest wall
Murmurs are also characterized by location, by which time in the heart cycle they occur, where they are the loudest, and whether they’re long or short. The specific details of a heart murmur will help your veterinarian identify what is causing the murmur and whether further diagnostics are needed.
Heart murmurs can be difficult to detect
It takes a skilled veterinarian to detect some heart murmurs. The severity of murmurs can vary from one exam to the next. Some cats will have murmurs as a result of stress. A mild murmur may be worse if a cat is dehydrated. If a cat is breathing hard, or if the cat’s human or a veterinary assistant are petting the cat during the exam, inexperienced vets may interpret the resulting sounds as a murmur. Murmurs may also be missed due to a poor quality stethoscope. Ideally, your vet should listen to your cat’s heart for a minute or two rather than just for a few seconds.
If a murmur is detected in a very young kitten, your vet may recommend a recheck exam after the kitten is four months old. While heart murmurs in very young kittens can be an indicator of a congenital defect, they can also be innocent murmurs that will disappear without intervention.
For an adult cat, further testing will be recommended, including radiographs, an electrocardiogram, and an echocardiogram (ultrasound of the heart.) If you vet suspects that the murmur is caused by another underlying disease, blood tests will also be required.
The most reliable test to diagnose heart disease is an echocardiogram with a Doppler examination. This specialized type of echocardiogram will measure the speed and direction of blood flow across the heart valves and in the heart chambers.
Some general practitioners will be able to perform ultrasound examinations in their clinics; however, reading a cardiac ultrasound properly requires advanced training. Anytime your cat is diagnosed with a heart murmur or other condition that affects the heart, a consultation with a veterinary cardiologist is recommended.
Treatment and prognosis
Treatment and prognosis will depend on the cause of the murmur and any underling disease processes, and may include a combination of medication, supportive care and continued monitoring. Prognosis will vary depending on the severity of the disease.
This post was first published in 2015 and has been updated.