You know that canine heartworm disease can be deadly — so you’re always certain to give your dog his monthly heartworm preventative tablet. Since he’s on the medication year-round, why does your vet insist on a heartworm test before she writes you an annual prescription? The answer lies both in sound veterinary practices and in law.


Heartgard for Dogs

  • Heartgard is a proprietary heartworm preventive medication that contains ivermectin, a broad-spectrum wormer that kills heartworms circulating in the bloodstream in the larval stage, preventing the larvae from growing into adult heartworms and invading the heart and lungs. Many veterinarians recommend Heartgard Plus, which also contains pyrantel. This wormer controls roundworms, hookworms and whipworms.

Legal Requirements

  • When you take a medication long-term, even if you experience no side effects, you still need regular visits to your doctor for a check-up before she will renew the prescription. The same holds true for veterinarians and their pet patients. Most heartworm preventatives require a prescription, and that means your vet must follow various state and federal regulations, including documenting an established veterinary and client relationship. For that purpose, your vet must conduct an annual physical examination, including testing for heartworm, before prescribing the medication.

    If You Missed a Dose

    • Most dog owners conscientiously give their pets a monthly Heartgard tablet, marking the calendar for the next dose date with the little red reminder hearts provided in the packaging. However, life happens. It doesn’t mean you’re a bad dog owner if you find you have one tablet left at the end of a year’s supply.Vacation, business trips, entertaining guests — all sorts of events can disrupt your schedule, causing you to lapse in giving your dog a tablet one month. During the period corresponding to that missed dose, your dog could acquire heartworm. While Heartgard is palatable to dogs, it’s possible that your dog might not swallow it or might cough up the chewable tablet shortly after administration without your knowledge.

    Heartworm Transmission

    • Dogs can’t pick up heartworm disease from other canines. Transmission occurs solely via mosquito bite. A female mosquito may carry baby heartworms or microfilariae, which she transfers to a host when she probes for blood. The heartworm larvae develop inside the host. When your vet tests your dog’s blood sample for heartworm, she’s looking for microfilariae or an antigen indicating the presence of heartworm. If your dog tests positive for heartworm, he can’t simply take the preventive — he needs special treatment that can require a period of inactivity. The latter requirement is especially difficult for young, energetic canines.

      How Do You Kill Heartworms in Dogs?

      Heartworm, a deadly parasite that can live in your dog’s heart and major arteries, is contracted through the bite of an infected mosquito. Should your dog be unlucky enough to contract heartworm, it will need to undergo treatment at a veterinarian’s office. While no over-the-counter treatment is available for a dog with heartworm, this preventative will help keep your dog from contracting heartworm.


        • Have your veterinarian confirm your dog has heartworm disease. A simple blood test will determine if the dog has heartworm microfilae (larvae) in its bloodstream.

        • Restrict your dog’s activity. This means no exercise, running or ball chasing. You need to keep your dog quiet because extra activity can cause the heartworm mass to dislodge and clog up the arteries, causing blockages and possible strokes.


  • Start your dog on a heartworm preventative as directed by your veterinarian. You may have to treat your dog over a two-month period.

  • Treat your dog with antibiotics and prednisone as directed by your veterinarian.

  • After two months have your veterinarian give the first shot of Immiticide. Your dog will likely stay at the veterinarian’s for a couple of days.

  • Continue to keep your pet quiet for a month.

  • Take your dog’s temperature daily. Contact your veterinarian if your dog’s temperature is more than 102.5 degrees F.

  • Bring your dog back to the veterinarian for the series of two shots of Immiticide.

  • Keep your dog on heartworm preventative medication.

  • Keep your dog quiet for a month with no exercise. Then follow with limited exercise but no running or jumping for two months.

    How Often Do Dogs Need to Be Tested for Heartworm?

    Heartworms are caused when larvae enters a mosquito when it sucks blood from another infected animal. Often, adult heartworms can live in a dog for 5 to 7 years. Heartworms usually cannot be detected in a dog up to 7 months prior to being bitten. It is very important to get dogs tested for heartworms at least once a year. Puppies can start on heartworm preventative from 6 to 8 weeks old. Most vets recommend putting dogs on a heartworm medication such as heartguard that is taken once a month.

    When Should My Puppy Begin Heartworm Medication?

    When to Begin

    • According to Drs. Foster & Smith, puppies can be given certain types of heartworm medication at 4 weeks old. However, Petco recommends beginning a regular heartworm regimen when a puppy is between 6 weeks and 6 months old. Additionally, it is always important to talk with your veterinarian about when to begin a heartworm prevention program and which program to choose. Some medications require blood tests prior to prescription.

      If your puppy is over 6 months old and is not on a regular heartworm prevention regimen, she may already have heartworms. It is important to talk with your veterinarian about getting medication for your puppy immediately. In this case, the vet will perform a blood test before giving you any medication to be sure that your puppy does not already have heartworms. According to Petco, dogs with pre-existing heartworm that begin taking medication can suffer from anaphylactic-shock reaction (a type of severe allergic reaction). Treatment for dogs suffering from heartworm is available in injection form. However, it can be expensive, may require a hospital stay and is potentially toxic.

    Time of the Year

    • It is a general rule that if you are being bit by mosquitoes, your dog is too. However, veterinarians recommend that dogs be treated with heartworm medication all year long since some medications also prevent things like intestinal parasites. As Drs. Foster & Smith points out, staying on a regular regimen decreases the chances of forgetting to give your puppy the medication. If you would rather give your puppy medication only during warm months when mosquitoes are out, Dr. Foster & Smith recommends giving the medication after you see the first mosquito. It is recommended to stay in contact with your vet, who will determine the length of time your puppy should take heartworm medication.