Miramonte Veterinary Hospital
1766 Miramonte Ave, Mountain View 94040   650-962-8338
Canine Heartworm Disease & Prevention
Accredited since 1996
foothills becoming one of the most heavily affected areas of the U.S.

The adult heartworm is large, up to 12” long, and lives predominantly in the pulmonary arteries
(pulmonary arteries carry blood from the heart to the lungs).  Infection causes the pulmonary arteries to
become inflamed and thickened which increases the work the heart must do to push blood past the
worms to the lungs.  Signs of disease range from exercise intolerance and coughing to heart failure.  
Therapy to kill the adult worm is available but is associated with mild to severe side effects primarily due
to the dead heartworms producing a severe reaction in the lungs.

Heartworm infection is clearly better to be prevented than treated.  Prevention is best begun at eight
weeks of age.  We currently recommend heartworm prevention for all dogs traveling outside urban bay
areas and for dogs living near or in the hills.  There are three choices available for prevention of
heartworm disease.

Heartgard (Ivermectin) and Interceptor, Sentinel (milbemycin oxime) are chewable tablets given
monthly.  Sentinel has the added advantage of controlling roundworm and hookworm infections and it
also contains lufenuron (Program) for non-insecticide flea control.

Revolution (Selamectin) is a liquid applied to the skin on a monthly basis, which is then absorbed into
the body.  Revolution is also effective against adult fleas, most ticks, hookworms, roundworms, and ear
and mange mites.

Your choice of heartworm prevention depends primarily on your choice for flea control and also on
convenience.  Sentinel and Revolution have the advantage of controlling fleas in addition to heartworm
prevention.  While the choices can be confusing our veterinarians and staff can suggest the prevention
best suited to your dog’s lifestyle and your personal preference.

In California, heartworm preventatives are typically administered year round as the hard frost season is
short.  Heartworm testing should be performed in all dogs older than six months of age before instituting
preventative.  Yearly re-testing is not recommended with year round preventative use unless you suspect
a monthly treatment was not given.