When the adult heartworms die, they are carried to the lungs by the pumping action of the heart. However, cats' pulmonary arteries are so much smaller than that of dogs, that a few worms can cause total arterial obstruction and death within a few minutes. Another approach is to treat the signs of heart failure, put the cat on a drug to prevent further heartworms from developing, and wait 1-2 years for the adult worms to die of old age. This approach is not without failure because a heartworm-infected cat can develop a pulmonary artery obstruction at any time and die acutely. However, one situation exists that does make the drug treatment more desirable, when the signs of heart failure cannot be successfully controlled, and the cat is obviously declining.
Dogs commonly receive one of several drugs to prevent heartworm infection.
However, none of these are currently approved for use in cats. But because these drugs are generally considered safe and effective, there are growing numbers of experts who suggest routine administration of heartworm prevention drugs to cats with potential exposure to mosquitoes, especially if they have had heartworms in the past.