This is video clip of Heartworm larva swimming in the blood of a dog seen recently at Montana Veterinary Specialists.
Heartworm disease is a serious and potentially fatal condition caused by parasitic worms living in the arteries of the lungs and occasionally in the right side of the heart of dogs, cats and other species of mammals. Dogs and cats of any age or breed are susceptible to infection. Infection can be prevented with a monthly heartworm preventative. Learn more at http://www.heartwormsociety.org/pet-owner-resources/heartworm.html