Heartworms are exactly what they sound like - worms that live in the heart.  These pesky critters cause a serious problem - heart failure and even death.  The good news is no pet needs to suffer from heartworm disease.  It is easily preventable.

Mosquitos carry heartworms in a larval stage.  When the mosquito bites a pet, the larvae end up in the pet's bloodstream.  There the larvae must go through several different stages before they become adult worms that can attach inside the heart.  This process takes about six months. This is why we can administer heartworm preventative only once a month.  The medication kills any larvae transmitted during the previous month before they get to the adult stage.  If you are a little late giving your dog his monthly preventative, consult your veterinarian as you may still be able to administer the medication for that month.  However, if several months go by with no prevention administered, a blood test should be performed before resuming the medication.

Yearly blood testing is important to be sure your dog did not get heartworm disease in spite of your best efforts.  You may have been late a month or skipped a month entirely without realizing it.  Perhaps the dog vomited after the medication was given or spit it out when you weren't looking.  If you are unable to give your dog the preventive medication, testing becomes even more important.  Heartworm disease is treatable, but only if it is caught early.  Once heart failure occurs, the dog may not survive the treatment.