or more appropriately

What are Heartworms?

Heartworm disease is a serious and potentially fatal condition caused by parasitic worms living in the arteries of the lungs and in the right side of the heart of dogs, cats and other mammals, including wolves, foxes, ferrets, sea lions and (in rare instances) humans. Heartworms are classified as nematodes (roundworms) and are but one of many species of roundworms. The specific roundworm causing heartworm in dogs and cats is known as Dirofilaria immitis.

Dogs or other animals harboring adult worms are the recognized reservoir of infection. Adult worms produce the offspring that circulate in the blood and are then transmitted to mosquitoes once they bite the infected animal. These offspring (microfilariae) undergo development to an infective larval stage within 14 days in the mosquito. At this time they can be transmitted to another host (such as a cat or dog) when the infected mosquito bites again. The infective heartworm larvae travel through a tubular organ within the mosquito’s head and are injected into the skin of a new host animal through the mosquito bite wound. In the dog, the larvae progress in their development to an adult form of the worm and live in the heart and pulmonary vessels, where they continue the life cycle and cause extensive injury. In the cat, the larvae molt as well, but fewer worms survive to adulthood. While dogs suffer severe heart and lung damage from heartworm infection, the cat’s primary response to the presence of heartworms occurs in the lungs.

Within the dog, the time frame between initial infection and growth to adult worms is approximately six to seven months, eventually arriving in the heart and pulmonary vessels where they begin to produce new offspring. This period is referred to as patency. In cats, it takes seven to eight months before adult worms arrive in the heart and pulmonary vessels, and this is referred to as transient patency. In most cases the life cycle of the heartworm ends here, since microfilaria are produced in less than 20% of cats. Some worms may get up to 4 inches long in a cat and 12 to 14 inches long in a dog.

Heavy infestation of heartworms will cause swelling in the lungs, pulmonary arteries, kidney and heart, which will eventually cause the animal to die.  It can also cause anemia and liver damage. For more about the life cycle, read this article:  http://www.heartwormsociety.org/download/HeartwormLifeCycle.pdf

Symptoms may include —

  • Loss of appetite
  • Lethargy
  • Coughing        
  • Weakness       
  • Hemorrhage

For both dogs and cats, clinical signs of heartworm disease may not be recognized in the early stages. This is because the number of heartworms in an animal tends to accumulate gradually over a period of months and sometimes years and sometimes after repeated mosquito bites.

Recently infected dogs may exhibit no signs of the disease, while heavily infected dogs may eventually show clinical signs, including:

  •          A mild, persistent cough 
  •          Reluctance to move or exercise          
  •          Fatigue after only moderate exercise
  •          Reduced appetite and weight loss

A note about Cats:  Cats may exhibit clinical signs that are very non-specific, mimicking many other feline diseases. Chronic clinical signs include:

  •          Vomiting 
  •          Gagging 
  •          Difficulty or rapid breathing
  •          Lethargy  
  •          Weight loss   

Signs associated with the first stage of heartworm disease, that is when the heartworms enter a blood vessel and are carried to the pulmonary arteries, are often mistaken for feline asthma or allergic bronchitis, when in fact they are actually due to a syndrome newly defined as Heartworm Associated Respiratory Disease (HARD).

Heart Failure

Blood is usually pumped through the arteries of the lung. When the arteries are plugged with worms, the heart must pump harder against the pressure of the plugged arteries.  This is called pulmonary hypertension.  The right side of the heart must work very hard to pump the blood. There is less space in the pumping chamber for the blood to be pumped if the worms begin backing up into the heart.  Using less blood than normal, the heart must pump through the high pressure system of the plugged arteries.  The heart has to pump more diligently in order to meet the oxygen demand. 

When a heart muscle is overworked it begins to thicken.  When this happens it may not conduct electrical impulses as it should.  This means arrhythmia can happen as the pumping/filling action may be disrupted.  When arrhythmia begins, sudden death is a possibility. 

Fluid may accumulate in the chest cavity and abdominal cavity if the right side of the heart becomes too weak. This leads to a pot bellied appearance (Caval Syndrome) and / or difficulty breathing.

Chronic Immune Stimulation

When a heartworm-positive dog goes without heartworm treatment, its immune system becomes chronically stimulated.  Antibodies, which are important tools of the immune system and inflammatory proteins, are produced in high amounts all the time.  These antibodies can cause problems by precipitating in the delicate membranes of the eye, kidney, blood vessels, and joints. Antibodies that are stuck in these problem areas, call in the inflammatory cells and damage these delicate membranes.  Therefore, this action will cause tremendous tissue damage and pain.

Caval Syndrome 

Caval Syndrome represents an especially disastrous form of heartworm disease. There are so many worms residing in the right side of the heart (around 100) that the entire right side is filled with worms and they are backing out into the large veins that feed the heart. Usually there are no signs of heart disease prior to the collapse, shock, and red blood cell destruction associated with this syndrome. Death usually occurs within 1 to 2 days.  If Caval Syndrome is present, Amber Technology highly recommends taking your dog to the veterinarian for treatment to open the dog’s jugular vein and physically remove the worms with a special clamp. If enough worms can be removed to re-establish blood flow, the dog may survive.

Heartworm disease is a highly significant problem and must be managed both by dealing with the worms and by dealing with the heart disease.


Killing heartworms can be dangerous for your animal. Dead worms can clog small blood vessels causing organs to fail. It is imperative that you confine your animal to a small space to try and prevent this from happening.

You need to remember that these are HEART WORMS.  The heart is a vital organ.  Whenever someone works with the heart there is a large risk.  The heartworms can dislodge and depart anywhere in the system.  The heart can become weakened from the heartworms.  Heartworms can get up to 1 foot long.  If a dog is harboring a 1-foot long heartworm, the time to rid the body of the heartworms can take 36 weeks or longer.  The severity of the heartworm infestation and the condition of the heart determine the results of the treatment.