Both dogs and cats are susceptible to a blood borne parasite transmitted by mosquitoes that can develop into worms which live in the heart. This disease is life threatening and much easier to prevent than treat. Infected dogs initially will show no symptoms and only late in the disease course will dogs develop symptoms including coughing, exercise intolerance, and weight loss. Cats are infected much less commonly and will often have vague symptoms such as occasional vomiting and lethargy. Middlesex County Animal Hospital recommends yearly blood screening for heartworm disease in dogs and a year round monthly parasite prevention medication. These medications not only prevent heartworm disease but will also control intestinal parasites. Monthly prevention can also be given to at risk cats.