Heartworm Preventative Reviews



There are over a dozen products available for your dog and cat for heartworm prevention. There are oral forms, topical forms, and even an injectable form. With all those choices, how do you decide which is the best for your pet? Using my knowledge and experience as a veterinarian and feedback I have received from clients, I intend to provide you with valuable information regarding various heartworm preventatives. My hope is that by showing my perspective, you will be better able to make an informed decision about your pet’s health.


Heartgard was one of the first heartworm products on the market. The name is familiar and fits its purpose to guard the heart. The active ingredients include ivermectin and pyrantel pamoate. Ivermectin is the ingredient that eliminates the immature heartworms in the dog’s body. The pyrantel pamoate is effective against common parasites like hookworms and round worms

PROS: It is easy to give to dogs because it is shaped as a beef flavored treat and is rather palatable. I have not heard many complaints by owners about giving the medication. Side effects are not common with Heartgard but they exist according to their label. I have yet to receive a complaint about any side effects from my clients. The costs are reasonable with an average of $60-$90 dollars a year depending on the size of your dog. This comes out to about $5-$8 a month. This can be an affordable option for many.

Cons: The shape of the pill is a rectangular shape which can be easy to give to larger dogs but is sometimes challenging to give to smaller dogs. The deworming component of the drug is not as broad spectrum (does not treat as many intestinal parasites) as other heartworm preventions on the market. There are other products that in addition to treating the same intestinal parasites also treat whipworms and tapeworms. These products will be mentioned further on in the review.

Sentinel Small

Sentinel is a monthly flavor tab which prevents heartworm disease and controls flea population in dog and puppies. It was manufactured by Novartis the company that used to make Interceptor. Interceptor was one of Heartgard’s biggest competition. Sentinel and Interceptor was off the market for a few months due to a problem at one of their factories that halted production. When that was corrected, Novartis discontinued Interceptor and just marketed Sentinel instead. Now Elanco plans to market Sentinel because of its acquisition of the company last year. The active ingredients include Milbemycin oxime and lufenuron. Milbemycin oxime eliminates heartworm larvae, hookworms, roundworms, and whipworms. Lufenuron breaks the flea life cycle by preventing the development of eggs. It does not have any action on adult fleas.

PROS: It has a broad spectrum for deworming against intestinal parasites. It helps control fleas with it’s active ingredient Lufenuron. The pills are a reasonable size and shape which allows for easy administration to dogs big or small. It is also reasonably priced with costing between $65-$120 a year depending on the size of the dog. This is about $7-$10 a month which is close to what Heartgard costs,

CONS: Clients are sometimes confused by how Sentinel helps with flea control. Some think that they have complete flea control and therefore forego purchasing an additional product that kills adult fleas. Of course this is not the fault of the Sentinel brand.


Trifexis is one of the first products to combine a monthly heartworm and flea prevention in one pill. It became very popular especially when Sentinel was off the market. At the time, it was one of the few products that could replace Sentinel with regards to flea control and as a broad spectrum dewormer. The active ingredients include spinosad and milbemycin oxime. The spinosad kills adult fleas usually within an hour after ingesting the pill. Milbemycin oxime is the same active ingredient as in Sentinel.

PROS: Trifexis is one of the most broad spectrum products on the market. It is the only oral heartworm preventative that also kills adult fleas. Clients find this convenient because they don’t have to worry about buying separate products for flea and heartworm prevention. This saves them money in the long run when compared to buying the products separately.

CONS: One of the biggest negatives about Trifexis is its side effects. Vomiting is the most common side effect reported by clients. This usually happens when this is given on an empty stomach. Some clients have also complained that after giving their dog a pill they started acting “funny”. Side effects seem to be more prevalent when changing from a lower dose to a higher dose because of a change in weight. Clients also complain that they have trouble administering the medication because of the large size of the pill. Because of this many find it extremely challenging to give this pill to smaller dogs. Trifexis was also been in the news in the past because of claims it caused very serious side effects in some pets. This publicity and resulted in some loss in popularity. I have seen none of the serious side effects claimed by the various news and social media reports, but many of my clients have decided to stop using Trifexis. Overall most clients who have used Trifexis haven’t had any problems and have found the product to work great. But I definitely have seen more side effects with Trifexis compared to the other products. Trifexis also has no label claim for effectiveness against ticks. Though it is believed to protect against some ticks for up to 2 weeks.


Proheart by Zoetis is the only FDA approved injectable heartworm preventative. One injection is given and provides 6 months of heartworm prevention. The active ingredient in Proheart is moxidectin which is time released through sustained microspheres.

PROS: Proheart is extremely convenient. One injection last six months so you have one less thing to worry about each month. This is helpful for clients who have trouble remembering to give medications monthly. This also guarantees that your dog will be protected for at least six months, so compliance is %100.

CONS: The active ingredient moxidectin only treats heartworms and hookworms so its spectrum of treatment is limited in comparison to the other preventatives. Some clients forget to repeat the injection performed 6 months later because of the length time in between treatments. Though infrequent there is a potential for side effects like swelling of the face or at the injection site. In the majority of these cases, this can be easily treated and if reported Zoetis may cover the costs.

Advantage multi

Advantage Multi by Bayer is a monthly topical product that is not only a heartworm preventative, it is also a broad spectrum dewormer and flea preventative. It contains the active ingredients imidacloprid and moxidectin. The imidacloprid kills fleas and the moxidectin handles the rest of the parasites. It is even labelled to treat scabies.

PROS: Advantage multi is one of the most broad spectrum topical products out there. It takes care of both fleas and heartworms so you only have to worry about one product. It is also a broad spectrum dewormer effective against hookworms, roundworms, and whipworms. Overall some money can be saved since there is no need to buy a separate flea and heartworm product. The fact that it is topical can be beneficial when a pet is difficult to give pills too.

CONS: One negative is as with most topicals you have to remember not to bathe your dogs for at least 48 hours after the application of the product or it might lose its effectiveness. It also has limited tick prevention, so it may not be the best choice if you are dealing with a heavy tick infestation.


Revolution is another topical monthly preventative that is indicated for heartworms, fleas, ear mites, scabies, and limited tick prevention. The active ingredient is Selamectin. This product is also very popular for cats.

PROS: It does provide an advantage that you only have to worry about one product for fleas and heartworms..

CONS: Revolution unfortunately does not have the greatest tick coverage. It is only labelled to be effective against one tick Dermacentor Variablis aka American brown tick. Also in dogs it is not labelled to treat any intestinal parasites though it has great coverage in cats.

This table below summarizes the actions of the products:

Actions AgainstHeartGard
Advantage Multi
Advantage multi
Roundworms/hookwormsYesYesYesHookworms onlyYesNo
Flea ControlNoYes (stops egg production only)YesNoYesYes
TicksNoNoYes (limited tick species and time period)NoYes (limited tick species)Yes (limited tick species)


In summary all the products above are effective for preventing heartworm in your pet. There is no noticeable advantage between the types of products in regards to this. Whether you choose an oral, injectable, or topical product will depend on you and your pet’s preference. The products that have a broader spectrum could save you some money, especially if you only have to by one that treat heartworms and fleas. There is an alternative to deal with these products that have limited tick efficacy. A tick collar like Preventic can be used. Also many of the companies offer reminders via text or email to help one remember when to give the prevention.


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