Heartworm in cats is a serious and potentially life-threatening condition that occurs when a kitty is bitten by a mosquito that's infected with the worm parasite Dirofilaria immitis. While outdoor cats are more at risk for infection, indoor cats are also susceptible to heartworm disease since mosquitoes can easily infiltrate the barriers of doors and homes.
Luckily, there are several medications for cat heartworm prevention. Additionally, by knowing the signs of heartworm, you can ensure your kitty stays safe from this vicious disease.
Heartworm in Cats: What Is It?
Cats become infected with the heartworm parasite if they're bitten by a mosquito carrying heartworm larvae (immature worms). Then, the larvae mature and migrate from the bloodstream to their final residence in the heart and lungs of a cat. The death of these heartworms can result in a severe inflammatory reaction, which can be fatal for cats.
It's possible for signs of heartworm in cats to develop prior to the parasite reaching maturity, due to an inflammatory response in the lungs triggered by the larvae. In most cases of heartworm disease in cats, there are often only a few adult worms present. However, since the size of a cat's heart and blood vessels are smaller than those of a dog, the damage caused by the worms is significant.
Despite its name, heartworm disease in cats does affect the heart but it primarily attacks the lungs. As such, a new term has been coined to describe heartworm in cats: heartworm associated respiratory disease (HARD), reports American Veterinarian.
Some cats are able to clear the heartworm parasite through an immune response to the worms. However, even if this occurs, signs commonly seen with the disease may still occur. For most cats who have been bitten by an infected mosquito, the heartworm larvae will mature and migrate, resulting in several overt signs.

What Are the Symptoms of Heartworm in Cats?
The most common symptoms of heartworm in cats mimic those of feline asthma and other chronic respiratory diseases. These signs can include intermittent coughing and increased breathing rate and effort.
Signs of heartworm disease in cats can also be vague and general in nature and include mild lethargy, intermittent vomiting, weight loss and decreased appetite.
How Is Cat Heartworm Diagnosed?
A veterinarian will diagnose heartworm in cats by considering the pet's health history, physical exam findings, radiography of the chest and general blood work. A vet will also need to perform specific blood tests to evaluate for the presence of heartworm antibodies and adult heartworm antigens or proteins.
An echocardiogram (an ultrasound image of the heart) can be performed to see if there are adult worms in the heart and associated blood vessels. According to the Cummings School of Veterinarian Medicine at Tufts University, this noninvasive form of imaging can also evaluate if your pet has any other heart problems, such as valve abnormalities, tumors, dilation or muscle thickening.
A cat may need to undergo multiple tests to confirm the diagnosis of heartworm disease.