Heartworm, or Dirofilaria immitis, is an internal parasite that lives in the bloodstream of infected animals, and matures into adult worms within their heart and pulmonary (lung) arteries. Heartworm is passed from infected animals to non-infected animals through mosquito bites and can occur in both dogs and cats. The immature heartworm, or microfilaria, will live within the infected mosquito bite and then the skin for up to several months while it is maturing into a larval form. Once mature, it then travels into the blood and then heart. Mature worms in the heart of affected animals can reach up to 35 cm in length and can end up causing significant damage to the heart and lungs. Symptoms of infection include coughing, exercise intolerance, laboured breathing and weight loss, however, many animals do not show any sign of infection. If left untreated, heartworm can be fatal. For this reason, it is important to ensure that your pet is protected against heartworm during the months of the year that mosquitos are present in areas where heartworm is prevalent. To learn more about heartworm testing and prevention, speak with your veterinarian