What You Should Know About Heartworm Disease

Adult heartworms are spaghetti-shaped parasites that live in blood vessels in the heart and occasionally within the lungs. Mature female heartworms release offspring called microfilariae into the blood stream. Microfilariae are tiny –small enough for a mosquito to ingest when the mosquito takes blood from an animal. Mosquitoes transmit heartworms from animal to animal. Although heartworms can occur in cats, they are much more common in dogs.  Microfilariae develop for six months in dogs and eight months in cats before they become adult heartworms capable of releasing microfilariae into the blood stream. During this time, the microfilariae migrate through body tissues until they reach the heart and blood vessels of the lungs.  Heartworm disease is the syndrome caused by the body’s response to adult heartworms in the heart and blood vessels in the lungs.


Heartworm infections are usually diagnosed by your veterinarian with a blood test. X-rays, EKGs, Ultrasound, blood and urine tests are useful in assessing the severity of the disease.

Heartworm Disease

Your pet has heartworm disease. Heartworms cause a serious and sometimes fatal disease of the heart, lungs, and other organs. Common clinical signs include coughing, difficult breathing, and exercise intolerance.  Heartworm disease can be cured with drugs to rid your pet’s heart of adult worms and blood stream of microfilariae. This client education sheet will help you learn more about heartworm disease and will review your veterinarian’s instructions for your pet’s care at home, as well as follow-up with the veterinary health care team.

Treatment and Home Care

Drugs are used to kill the adult heartworms. During this phase of therapy, your veterinarian may hospitalize your pet. Medications to strengthen the heart and remove fluid may be necessary. When your pet goes home after adult heartworm therapy, you will need to strictly confine it for another month to prevent fragments of dead adult heartworms from obstructing blood vessels in the lungs. Fever, coughing, lethargy, and, in severe cases, coughing up blood are signs

that this has occurred.  Drugs are also used to kill the microfilariae. Pets can be protected from heartworm infection with preventive medications. These medications should only be given after an animal tests negative for heartworm. Preventive medications are formulated so that some medications are given daily, monthly, and others at 6 month intervals.

Nutritional Plan

Because heartworms can affect an animal’s heart, lungs, liver and kidneys, your pet may present with signs of organ failure and fluid accumulation in the chest and abdomen. If your pet has fluid accumulation or signs of failure in one or more of these organs, your veterinarian may give you special feeding instructions. Foods with reduced levels of protein, phosphorus, and sodium may improve organ function and help eliminate excess fluid in the chest and abdomen. After your pet’s recovery is complete, your veterinarian may suggest another dietary change based on your pet’s age and body condition, and on the presence or absence of disease in other organs and body systems.

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