Monash Veterinary Clinic

Visit Us

Monday - Friday: 8.30am - 7pm

Saturday: 8.30am - 1pm

Sunday: Closed

Please note, we are closed from Sunday 24th December, we will reopen on Wednesday 27th December at 8:30am.

Heartworm Advice

Heartworms are white thread-like worms which grow to 12-30cm long. They live in the heart and the large arteries in the lungs.

Heartworm is spread by mosquitoes. A mosquito bites an infected dog drawing up immature heartworms (microfilaria) which are then transmitted into the susceptible dog. The immature heartworm takes 5 months to develop into an adult heartworm. Once a dog has several mature heartworms in its heart the clinical signs of disease develop.

Clinical signs of the disease are:

  • Exercise intolerance
  • Coughing
  • Distended abdomen
  • Poor coat and illthrift


Diagnosis of heartworm disease is carried out by a simple blood test at the clinic. In most cases a simple smear or concentration test is used. This test determines the presence of microfilaria. A more sophisticated blood antigen test may be required at times.


Treatment of heartworm disease is quite effective in all but severe cases. It requires the patient to be hospitalised for 2 days whilst injections are given to kill the adult worms. The patient is then checked 1 month after this and if there are no microfilaria present in the blood the patient is started on preventative treatment. Before starting heartworm preventative medicine, adult dogs must be checked for the presence of microfilaria in their blood.


Prevention of heartworm disease is carried out by administering either an annual injection of PROHEART, a monthly tablet such as INTERCEPTOR or SENTINEL or a monthly spot-on such as REVOLUTION. Regular intestinal deworming preparations such as Drontal or Canex Multi Spectrum have no effect on Heartworm.

Proheart injection protects only against heartworm and is usually given with the annual vaccination. Proheart stops the worry of giving monthly tablets. Puppies should commence heartworm preventative treatment at 3-4 months of age. They do not require a blood test before starting heartworm preventative treatment if they are less than 6 months old. It is best to treat your dog permanently as mosquitoes can be found all year round in most parts of Melbourne.

There are 2 types of monthly tablets that we recommend:

Interceptor spectrum: Interceptor is a flavoured chew given once a month that not only prevents heartworm, but also eliminates all intestinal worms.

Sentinel Spectrum: Sentinel is a flavoured tablet given once a month to prevent heartworm and eliminate all intestinal worms. Sentinel also helps with controlling flea burdens by sterilising the adult fleas so that they cannot go on to reproduce.

Revolution: a spot-on that protects against fleas, sarcoptic mange, ear mites as well as heartworm.

If you have an adult dog that has never been on heartworm prevention or you have missed a scheduled heartworm prevention dose in your dog, please contact the clinic for advice regarding testing or appropriate course of action. Recommencing heartworm prevention in these instances may be detrimental to the health of your dog.