Heartworm is on the rise in Arizona. Please use a preventive med as the treatment is horrid, not to mention pricey. Trust me,I know.
If you search "Heartworm in Arizona" you'll get lots of information.

I'm in AZ and can 2nd that Heartworm is very serious here. The prevenative only needs to be given once a month and usually you can find better prices online!

A couple of years ago we treated a dog that moved to TN from AZ. They had always lived in AZ and the owner had been using an online company that was not providing quality preventatives. Heartworm preventative should not be that expensive, no more than $12 a month per pill for a dog between 50-100 lbs. If your pills are that expensive check with petmeds or call some clinics.
I provided you with a link for heartworms, and the best reason I can give you to keep giving them. By not giving preventative you are putting your dog at risk. There is nothing worse than seeing or hearing a dog with worms coughing and gagging day in and day out. Imagine if you had a chest full of worms, your comfort would be minimal. Treatment for this condition can be very dangerous and is very expensive. For a large dog this can cost upwards of $350 and may require 2 treatments. The medication used to treat is very expensive and the recovery time must be done with minimal activity and excitement.

It is much cheaper, kinder, and more responsible to prevent than to treat. Hope this helps!

Here is a link that might be useful: http://www.heartwormsociety.org

I don't recall which online company it was but fairly recently I heard about one that just got a huge judgement against them for selling inferior products. Also I don't know how the manufacturers would deal with products being bought online but if they are purchased thru your vet and documented thru the medical records that your dog has had sufficent product bought, then if your dog gets heartworm the manufacturer will pay for the treatment. And dogs do get heartworms sometimes when they are on the preventative. Maybe they don't swallow a pill or there is some speculation that immunity to the preventatives is begining to develope in some areas.

Lisa

Ask your vet if they will match prices.
Some time ago I faxed over the form to my vets office so I could order from Drs F & S ans they said they were concered the online sources were not the same and agreed to match the prices. (and did)