While the term "grade 3 heart murmur" might strike fear in your heart in reference to Kitty, don't panic. It's quite possible that your cat is just fine. The murmur isn't the problem, but it indicates there could be an issue with your cat's ticker. Further testing is necessary.
The normal beating of a cat's heart creates a lub-dub sound, as heard through your vet's stethoscope. If a cat's heart doesn't make that sound, it might or might not be problematic. Heart murmurs result from additional blood flow to the heart. Generally, cats with higher grades of heart murmurs have other physical symptoms if your vet suspects a cardiac issue. These might include weight loss, lack of appetite, trouble breathing, pale mucous membranes and lethargy. Heart murmurs in kittens often disappear by the time of puberty, about 6 months of age.
Vets grade heart murmurs on a scale of 1 to 5, from the barely audible grade 1 to the very loud grade 5. According to Claws and Paws Veterinary Hospital, a veterinarian listening to a cat's chest with her stethoscope can barely hear the grade 1 murmur but clearly makes out the grade 2. The grade 3 has an intermediate loudness, while the grade 4 is very loud, even if the stethoscope barely touches the chest. She can feel it by placing her hand over the cat's heart. The grade 5 murmur can be heard without using the stethoscope. The Merck Veterinary Manual states that murmurs are typically defined relative to timing, intensity and location, but also characterized by frequency, quality and configuration.
If your vet's detected a grade 3 heart murmur, the next step is finding out the cause. She'll conduct various tests, including a chest X-ray, which reveal the size and shape of the heart and major blood vessels. Blood tests reveal your cat's general health and whether any of his organs aren't functioning normally. She might perform an electrocardiogram, which detects heart rhythms. An ultrasound gives her a complete picture of the heart, including wall thickness and the presence of tumors. Depending on the results of your cat's tests, she might refer you to a veterinary cardiologist.
The tests should reveal any cause of your cat's grade 3 murmur. Possible reasons include a congenital heart defect, cardiomyopathy, anemia and certain infections. Even if the results of your cat's testing doesn't indicate any serious disease, it might mean that he can't be put under anesthesia for any necessary future surgeries. Treatment and prognosis depends on the diagnosis. For example, if you find a cat suffering from an extreme flea infestation, his anemia could be caused by blood loss and monthly topical flea and tick control and a healthy diet could cure him. A cat with cardiomyopathy, or thickening of the heart muscle, might be treated with medication. Even if your vet doesn't find anything specifically wrong with Kitty, keep your cat's life as stress-free as possible and take him to the vet regularly for monitoring.
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