Heart worms are parasites.  In their adult form, they pose a very serious threat to dogs.  These worm like parasites can infest a dogs heart and all of the large arteries that go to it’s lungs.  Mosquitoes  are the culprits as they carry the heart worm larvae.  It’s transmitted to dogs by biting them.  The season where heart worm infection is common is spring and summer when the mosquitoes are out. In some areas of the country, heart worm is a risk all year long. Symptoms include coughing, weight loss and lethargy. Unfortunately, this disease can be fatal.  The good news is that it’s very preventable.  If your dog is at risk for heart worm, your vet will suggest very affective pet medication to prevent this disease.