All cats over 6 months old should be tested for heartworms prior to starting prevention. To prevent heartworm disease, heartworm drug or medication need to be properly applied.

Heartworm Prevention Cats

What is the Best Heartworm Prevention for Cats?

Many cat owners do not realize how important heartworm prevention is for cats. Infection with adult heartworms nearly always causes death of the cat.  Did you know one mosquito can cause a fatal heartworm infection in cats?  One infected mosquito bite can deliver enough larva to develop up to 5 adult heartworms. Each heartworm is 12 inches long. Once adult heartworms are present in cats they are very difficult to treat safely.  Since we cannot prevent mosquito bites we have to protect cats from fatal heartworm disease by using regular prevention.

Current heartworm preventions are all from the same “family” of drugs. They belong to a group of “antibiotics” produced by different strains of Streptomyces species bacteria.  This group of drugs is known as the macrocyclic lactones:

1) Ivermectin this is the active ingredient in Heartgard For Cats

2) Milbemycin Oxime this is the active ingredient in Interceptor For Cats

3) Selemectin this is the active ingredient in Revolution For Cats

4) Moxidectin this is the active ingredient in Advantage Multi For Cats

At what age should I start use heartworm prevention for my cat?

Heartworm prevention should start as soon as the kitten reaches the minimum age or weight for the product you wish to use. Because heartworms are transmitted by mosquitoes any kitten can be infected at an early age.  Most heartworm preventions should be started before the kitten reaches 9 weeks of age.

Do cats need heartworm tests before starting preventions?

All cats over 6 months old should be tested for heartworms prior to starting prevention.

How do I choose the best Heartworm Prevention for my cat?

Heartworm prevention for cats comes in two forms; a tablet form and a topical form. If you find it difficult to give pills you may prevent a liquid treatment that you apply to the skin. If you are concerned about other pets licking and grooming each other a pill may be the preferred option. Heartgard and Interceptor come in a pill format for cats.  Revolution and Advantage Multi are topical treatments. All are given once a month.

Heartgard for Cats

Ivermectin is the active ingredient in Heartgard for Cats.  It is a very effective heartworm prevention for cats that must be given monthly.  It comes as a chewable tablet. The pill can be fed as a treat or broken up and mixed with the cat’s food.  The tablets must be chewed or broken before swallowing to ensure proper absorption of the ivermectin by the gut. This product also controls hookworms in cats.  For cats with fleas Frontline is also recommended.  Before giving Heartgard to cats they must have a negative heartworm test.

Interceptor Flavor Tabs for Cats

Milbemycin Oxime is the active ingredient in Interceptor.  These oral flavor tabs may be fed to the cat by hand, mixed with the food or given to the cat as a pill. Interceptor Flavor Tabs also provides effective control of hookworms in cats.  It can be given at 6 weeks of age and is well tolerated and very safe.  Before giving Interceptor Flavor Tabs to cats they must have a negative heartworm test. Because of the difficulty of getting some cats to take the tablets it is not Dr Garner’s first choice of heartworm prevention for cats.


Selemectin is the active ingredient in Revolution.  Revolution is applied to the skin surface once a month.  It has minimal absorption into the body but cats tend to lick their skin and may increase absorption.  Revolution does control fleas, ear mites, roundworms and hookworms.  It resists removal by baths or shampoos.  Selemectin may not be as effective as other products for heartworm prevention.

Advantage Multi For Cats

Moxidectin is a remarkable substance that is both safe and effective as a heartworm prevention.  Advantage Multi is a topical solution for application to the cat’s skin once a month.

  • It is the only heartworm prevention that is effective against all strains of heartworms identified in cats
  • It is the only feline heartworm preventative that kills early L5 or juvenile heartworms as well as the L4 larval stage.
  • It kills hookworms, roundworms and ear mites in cats as well as controlling fleas

Dr Garner recommends Advantage Multi for Cats as the best Feline Heartworm Prevention Available today.  It has a broad range of effectiveness in cats against the different. life stages of heartworms. Advantage Multi effectively kills fleas and is also effective against more species of intestinal parasites and ear mites.  It is safer than others in the same category and can be given to kittens at 9 weeks of age or when they reach 2 pounds body weight.

Is it true that heartworms are becoming resistant to preventions?

There are concerns that heartworms are developing resistance. See this article that compares Advantage Multi to all the other common heartworm preventions.