Heartworm medication for dogs

How to Compare Dog Heartworm Prevention

Dog Heartworm Symptoms

Heartworm disease is a potentially life-threatening illness spread from animal to animal through mosquito bites. It is caused by a parasitic worm called Dirofilaria immitis. Young Dirofilaria worms, called microfilaria, circulate in the bloodstream of an infected animal. When mosquitoes feed on the infected animal, the mosquitoes pick up these immature, microscopic parasites. Within a couple of weeks, the microfilaria have matured within the body of the mosquito and are ready to infect another mammal. The next time the mosquito feeds, these young parasites, now called larvae, are injected into the next animal. This animal could be your cat or dog.

Once within your pet, the immature worms migrate through the body, eventually reaching the heart, lungs, and connecting blood vessels. In approximately six months, they grow to become adults as long as 14 inches in length. When they reproduce, their tiny offspring, the microfilariae, circulate in the bloodstream. At this point the cycle repeats and the worms can be spread to another animal by a mosquito bite.

The adult worms can live in your pet's body for many years. While there, they cause severe disease. Because these parasites live in the heart and blood vessels, the disease signs are those of heart and lung problems.

Dogs with heartworm disease may:

  • Tire easily
  • Cough
  • Lose weight
  • Have trouble breathing

As the illness progresses, animals may have fluid build-up in the abdomen and swelling of the legs. If not identified and treated, heartworms can cause cardiac failure and the death of the pet.


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Dog Heartworm Prevention

It is far wiser and much easier to prevent heartworm disease. This is done by administering medications to your pets that will kill larval heartworms if they are injected by a mosquito bite.

Several types of preventive medication are available for dogs, including tablets given on a daily basis, monthly tablets, and a monthly spot-on topical solution.

Animals should be on preventive medication whenever mosquitoes are present. In some areas of the country, pets may be kept on preventive medications year round, while in areas with cold winters, preventive may only need to be used during warm weather. Pets that are traveling from heartworm-sparse areas into warmer locations should also be on preventive medication.

Dog Heartworm Medicine

Dog Heartworm Preventives

Heartworm preventives are extremely effective. They will prevent heartworm disease if appropriately administered to your pets. Even dogs that do not set foot outside are candidates for the disease. The female mosquitoes that carry the disease are small enough to pass through screened doors and windows, and can infect indoor pets.

Dog Heartworm Treatment

Heartworm disease is treatable if diagnosed early, before severe heart and lung disease occurs. Diagnosis can be made with simple blood tests, but more sophisticated tests, including radiographs, angiography, and ultrasonography, may be used. Treatment involves injections of medication that kill the adult heartworms, specific drugs to eliminate the microfilaria, weeks of rest, and therapy as needed to control the medical problems that occur as a result of killing the worms. Treatment is typically successful and most pets survive.

Dog Heartworm Testing

Heartworm testing is a necessary, although sometimes confusing part of heartworm disease prevention. Testing is performed prior to placing a pet on heartworm preventive and to detect the illness in a sick pet. The tests check for the presence of adult heartworms.

There are many methods of testing, including several types of blood tests. A very common test, often done in the veterinarian's office, is called an antigen test. This test detects female adult heartworms that are at least six or seven months old. Other tests include blood smears to look for microfilaria and older, antibody tests.

All dogs should be routinely tested for heartworm disease. It is important to understand that the preventive should never be given without performing the blood test. Placing any animal on preventive that is already infected with heartworms can result in a severe reaction and the death of the animal.

Your veterinarian will advise you as to the proper time to test your dog. Testing is typically done on an annual basis, although some dogs may require more frequent testing.

Young dogs are not tested, but any puppies over six or seven months of age should be tested prior to starting preventive.

Dogs that are taking heartworm preventative for only part of the year should be tested each year prior to beginning preventive therapy. If the test is negative, the dogs should be immediately placed on preventive medication.

Dogs on year-round preventives are tested approximately once per year, at the discretion of the veterinarian.

Comparing Dog Heartworm Prevention


  Heartgard Plus Interceptor Plus Iverhart Max Iverhart Plus Revolution Dogs Sentinel Sentinel Spectrum Tri-Heart Plus
Heartworms X X X X X X X X
Fleas         X X X  
Hookworms and Roundworms X X X X   X X X
Whipworms   X       X X  
Flea Eggs         X X X  
Tapeworms   X X          
Ear Mites         X      
Ticks         X      


Updated September 14, 2020