Here is an illustration of what a heart infected with heartworms looks like: 
Heartworm Disease:

What is it:
Heartworm Disease develops when a pet becomes infected with parasites called Dirofilaria Immitis.  These parasites are transferred through the bite of an infected mosquito.  These parasitic roundworms reside in the pulmonary arterial system (lung arteries), and can also be found to migrate to the right heart and large veins.  Dogs may become infected by a few or up to several hundred heartworms.  Cats are similarly infected, although usually by only a few heartworms.  Heartworm Infection often leads to severe lung disease and heart failure and can damage other organs in the body as well. 

What it looks like:
How to Test:
We Heartworm test using antigen testing, as it is the most accurate test for detecting heartworm infection.  This test, seen below, takes just 3 drops of blood, 4 drops of conjugate, and the results take just 8 minutes.  The test that we carry also checks for 2 tick diseases, Lyme and Tick Fever.  The Heartworm test looks for the presence of small proteins released by the adult female heartworms into the petís bloodstream.  A positive test tells us that there are female worms present, and while a false negative is uncommon, they can occur if a pet has a male-only infection if only one for two worms are present or if the female worms are immature.  If you dog is showing signs of heart disease and the test is negative, the veterinarian will most likely recommend taking a chest x-ray or doing an ultrasound evaluation which can help identify heartworm disease.

How to Prevent:
We offer Iverhart Plus as our preferred Heartworm Prevention.  This is a once a month chewable tablet, than also protects your pet from hookworms, and roundworms.  They are typically sold in a 6 month supply, but up to 2 boxes can be purchased for a whole years worth of protection.  We currently offer $3.00 mail in rebates for every 6 month supply you purchase here.  This manufacturer (Virbac) gives the guarantee that that their product works.  If your pet comes up positive on heartworm test, virbac will cover the cost of treatment ONLY if you heartworm test your pet before starting the prevention, test yearly, and give the medication monthly. 
Why Test:
We recommend heartworm testing before you pet is put on heartworm prevention.  Only then if your petís results are negative should you start heartworm prevention.  It is important to test once a year after you pet is on the monthly heartworm prevention. If a heartworm positive pet receives heartworm prevention, a rare but very serious side effect could offur occur.  Adult heartworms produce millions of microscopic "baby" heartworms (called microfilaria) into the bloodstream. When you give a monthly heartworm preventive to a dog with circulating microfilaria, this can cause the sudden death of microfilaria, triggering a shock-type reaction. Even if your dog does not have this type of reaction, heartworm preventives do not kill the adult heartworms (although they may shorten the worms' life expectancy). This means an infected dog will remain infected with adult heartworms.
How itís treated:
Treatment for heartworms can be a very expensive, and, depending on the severity of the case, can also deadly due to a build-up of dead worms.  If a dog is infected with heartworms, the treatment needs to kill the adult and immature worms. Currently, only one product is approved by the FDA for this purpose (Immiticideģ- melarsomine hydrochloride). A series of this injection is given by deep injection into muscle.  For treatment, we, keep the pet here at the hospital for hospitalization as the Immiticide is being administered since there can be reactions.  Other medications may be given at the time of treatment depending on the stage of heartworm disease.
The signs of Heartworm Infection:
Typical signs of Heartworm Infection vary in severity, but include:
Tiring easily
Exercise intolerance
Weight loss
Rapid breathing
Coughing to the point of Fainting
Ribs become prominent
Chest starts to Bulge
Collapsing and Sudden Death
For more general questions and answers regarding Heartworm, please visit the American Heartworm Society.
The Complete Pet Animal Hospital
5135 N Dysart Road Suite 4
Litchfield Park, AZ 85340
Phone: (623) 935-9632
Fax: (623) 9359764

5135 N. Dysart Rd., Suite 4 Litchfield Park, AZ 85340
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(623) 935-9632
Clinic Hours
Moday: 8 am- 5:30 pm
Tuesday: 8 am- 5:30 pm
Wednesday: 8 am- 2 pm
Thursday: 8 am- 5:50 pm
Friday: 8 am- 5:30 pm
Saturday: 8 am- Noon