What is a sign my cat has heartworm?

So here's a trickier question than some people may think, 80% of cats are asymptomatic from showing signs of heartworms. So basically what that means is that they will not show any clinical symptoms. So remember eight out of 10 cats won't show symptoms, but the ones that do show symptoms, they'll usually have more breathing air issues kind of almost sounds like asthma, like wheezing or dyspnea. It can be very subtle sometimes, sometimes not, a little bit more aggressive, any panting. Anytime you see a cat pant, bring them in. Cats do not pant normally so you have them examined if they do. Other things that are more extreme, it's rare, but they could have a pretty aggressive nosebleed. Sometimes some cats can get something called thromboembolism, where they throw a blood clot and almost their back legs go cold and they can't really move them too much. So these are just some of the signs, but more respiratory signs you would see in a kitty cat.

Weight loss, open mouth breathing, coughing and labored breathing, and often vomiting. Cats tend to vomit with many different diseases. Cats develop symptoms much earlier than dogs because the immature stages arrive in the lungs earlier than in dogs. Dog symptoms are more geared towards adult worms being present. It's the immature stages, the earlier stages, that cause problems in a cat. Sometimes a few worms will make it to adulthood, and that's not a good scenario when that happens.

Cats with heartworms may show signs such as coughing, lethargy, lack of appetite, and even potentially sudden death.