Heartworm: Keep Your Dog Protected

by DFS-Pet-Blog on April 15, 2017

Cat Dog

How you do remember to give your dog his monthly heartworm pill? If you don’t have a good method, get one! Remembering to give your pet his heartworm pill is too important to not be on the ball with this one. Prevention is easy…treatment is not.

In a nutshell, a dog can get heartworm disease if bitten by an infected mosquito, and it effects the heart and lungs of a dog. At first, there are often no visible symptoms of heartworm disease in dogs. Prevention is simple: a veterinarian does a blood test to confirm that the parasite is not present in your pet, and a prescription is then written for a heartworm preventive.

The following excerpt has some important info about heartworm infection and prevention that every cat and dog owner should know. (Full heartworm article as written by the veterinarians at Drs. Foster & Smith.)

What damage do heartworms cause?


In dogs, the adult worms can obstruct the various large blood vessels leading from the heart to the lungs. Worms may also enter smaller vessels in the lung and obstruct those vessels, as well. In severe cases, called “caval syndrome,” worms start to fill the right ventricle of the heart.

What are the signs of heartworm infection and how is it diagnosed?

Most dogs with heartworm infection do not show signs of disease. Some dogs may show decreased appetite, loss of weight, and listlessness. Often, the first sign of the disease is a cough. Animals with severe heartworm disease will start to show lack of endurance during exercise. Some will accumulate fluid in their abdomen (ascites) that makes them look pot-bellied. In rare situations in which animals have many adult worms, the animals may die of sudden heart failure.

Blood testing is performed to identify dogs infected with Dirofilaria immitis, the heartworm parasite. Because blood tests are not always accurate, we need to interpret test results in relation to the history and the symptoms the animal is showing. Radiographs (x-rays) and ultrasound (echocardiography) are often performed to look for typical changes in the heart and lungs caused by D. immitis, and determine the severity of the infection. Changes include enlargement of the pulmonary artery and the right ventricle. Certain types of cells (eosinophils) may increase in the blood or secretions from the lungs in heartworm infections. These additional findings can all help support the diagnosis.

What is included in a good heartworm prevention program?

The best program for prevention of heartworm infection includes using preventives, performing routine heartworm testing, and reducing exposure to mosquitoes.

Heartworm preventives

Medications used to prevent heartworm infections are called preventives. The first thing to remember is that preventives are NOT used to kill the adult worms. Special drugs called adulticides must be used to kill the adults.  Some preventives can cause severe problems if given to animals with adult heartworms or microfilariae. Follow the recommendations of your veterinarian and the manufacturer of your preventive in regard to testing prior to giving the preventive.

A number of monthly heartworm preventives for dogs are on the market. Some heartworm preventives, or drugs that are combined with them, will control other parasites. Preventive products should be used year-round, even in areas where mosquitoes only occur seasonally. Even if doses are accidentally skipped, preventive products are still beneficial to the pet. If given consistently over a 12-month period, it’s possible to actually stop worms from developing into adults. Also, monthly heartworm preventives have activity against intestinal parasites, which inadvertently infect millions of people every year. These preventives protect pets and people.

The daily preventive, diethylcarbamazine is available with a prescription through compounding pharmacies. Two main disadvantages are that it can produce severe reactions if given to a dog with a heartworm infection, and that missing even two or three days of administration could result in a lapse of protection.

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July 28, 2010 at 8:20 am

{ 7 comments… read them below or add one }

Rosemary July 28, 2010 at 9:22 am

Personally, I miss Filaribits. It was SO much easier to remember a daily pill than a monthly one, or adjust the dosage as your puppy grew. I would just leave the bottle in the food conatiner, and put the pill(s) in the bowl(s) when I scooped out the food. Now, even though it is marked on my calander, I will often give the montly pill several days late. After I accidently gave Lucky a heartworm pill twice, thinking that I had forgotten, I now cross it off when I give out monthly heartworm/flea preventatives.

Living on the Gulf Coast, it is very important to keep up with treatment. Down here, if a dog hasn’t been on prevention, you can almost assume that it will have heartworms. Also, cats can get heartworms, so it is important to treat your cats too, especially if they go outside.

Deb July 28, 2010 at 9:27 am

That email reminder service is great! Just signed up to receive reminders for giving my dog his heartworm pills and for putting his flea and tick preventive on him. I never quite understood what the heartworm pills were exactly preventing, but after reading this I am going to make sure I don’t let his monthly pill get forgotten! Good info.

Peggy July 28, 2010 at 10:22 am

Oh I love that email reminder service, I’m going to sign up. I heard that it was dangerous to give your dog a pill if you’ve missed too long. How long is too long? Unfortunately, I’ve missed 3 months. Can I safely give her a pill now? If not, should I bring her to the vet for a heartworm test first? Thank you!

Dr. Scott A. McKay July 28, 2010 at 12:21 pm

Peggy, according to the American Heartworm Society, you should start giving your dog its monthly heartworm preventative right away and have your dog tested for heartworm disease in 6-7 months. The reason for testing is that it takes this parasite this length of time to mature into an adult heartworm. It is the adult heartworm that is detected when testing. Meanwhile the monthly preventative will kill-off any larval heartworms that may have been introduced by a recent mosquito bite. In addition, if you are using one of the broad spectrum monthly products that also targets intestinal parasites (Heartgard Plus, Interceptor, etc) your dog will benefit from that. Best of luck.

Deborah W. July 29, 2010 at 4:06 pm

It’s so sad to hear stories about pet owners who are cutting back on their pet’s routine medication, such has heartworm. I know a few neighbors that have had to make that tough decision. They both involve a spouse losing a job.

It’s very sad to hear, but I can understand. It’s either that or not having food on the table to feed their family. I just pray their dogs don’t get heartworm disease in the meantime. That would be tragic.

Ellen B. July 29, 2010 at 4:37 pm

Deborah, I agree, it is a heartbreaking decision. I must say that the economic times is one reason that Dr. Race Foster & Dr. Marty Smith decided to offer free shipping on all cat & dog pharmacy and healthcare products. They are really good people and have the best interest of pets in their heart. Thank you for your comment….sad but true.

brittany August 9, 2010 at 11:54 am

Do I need a prescription for my dogs’ heartworm meds to get them drs. Foster and Smith? my vet REALLY REALLY HATES it when I ask for a written scrip, so much so I won’t do it.

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