Heartworm FAQ

In this blog, we’ve answered some of our most frequently asked questions about Heartworm disease and the importance of prevention.


What is Heartworm Disease?

  • Heartworm disease is a serious disease caused by “heartworms” that results in severe lung disease, heart failure, other organ damage, and death in pets, mainly dogs, cats, and ferrets.

  • The worms are called “heartworms” because the adults live in the heart, lungs, and associated blood vessels. 

  • The heartworms are carried by mosquitoes from pet to pet.

How does my dog/cat get heartworms?

  • It only takes one bite from a mosquito for a dog to get infected with heartworms. 

  • Heartworm disease is not contagious, meaning that a dog cannot catch the disease from being near an infected dog.  Heartworm disease is only spread through the bite of a mosquito.

My pet is almost always inside, are they at risk?

  • Both dogs and cats are at risk of heartworms, whether or not they’re indoor or outdoor pets. Anywhere a mosquito can go, there is a risk. 

  • It’s important to be consistent and up-to-date with prevention.

Should my dog get tested?

  • Dogs that are 6 months of age and older should be tested for heartworms before starting heartworm prevention.

  • A dog may appear healthy on the outside, but on the inside, heartworms may be living and thriving. If a heartworm-positive dog is not tested before starting a preventive, the dog will remain infected with adult heartworms until it gets sick enough to show symptoms.

What happens when my dog is bit by an infected mosquito?

  •  In a newly infected dog, it takes about 6 to 7 months for the heartworm larvae to mature into adult heartworms. At that point, you may start seeing symptoms.  The adult heartworms mate and the females release their larvae into the dog’s bloodstream.

  • Inside a dog, a heartworm’s lifespan is 5 to 7 years.  Adult heartworms look like strands of cooked spaghetti, reaching about 4 to 12 inches in length.

What are the symptoms?

  • The signs/severity of heartworm disease depends on how long the dog has been infected and where the heartworms are in the body, and the degree of damage that has been sustained by the heart, lungs, liver, and kidneys.

  • The most obvious clinical signs of heartworm disease are a soft, dry cough, shortness of breath, weakness, listlessness, and loss of stamina.

  • All of these signs are most noticeable after exercise, when some dogs may even faint or become disoriented.


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Pet Vaccination Clinic provides efficient and professional care without losing the personal touch.

Dr. Stan Leland opened Pet Vaccination Clinic on June 1, 1985. Since day one, Dr. Leland has provided compassionate care, taking the time to explain animal care thoroughly to clients so they can champion their pet’s health. The Pet Vaccination Clinic is located at 1010 SW Military Drive in San Antonio, TX and offers multiple services including, but not limited to, vaccinations, flea and tick prevention, deworming, exams, health certificates, and heartworm preventative. Contact us here to make an appointment.