Adult heartworms in arteries and veins of a dog.

A 5-year-old terrier-type dog with a 3-week history of progressive lameness, swelling, and pain in the left hindlimb suddenly became paralyzed in the right hindlimb. Because of a poor prognosis, the dog was euthanatized. Necropsy revealed mature heartworms (Dirofilaria immitis) in the femoral arteries as well as in the right side of the heart and pulmonary arteries. Extensive ischemic necrosis in the muscles of the hindlimbs was attributed to occlusion of the femoral arteries by heartworms.