[Carina43]

DEFINITELY give the monthly Heartgard (not the shots.) It is not expensive. I took in a dog last year with HW; let me tell you treating it IS expensive! Not to mention HW will kill a dog.
Your dog will need an annual blood test (under $100) and the pills cost me about $40 for 6 months.

It cost me about $1000 all told to treat Dutch (I've seen costs both higher and lower than that.) The modified arsenic shots were painful and really kicked his butt for a while. He has to stay on the Heartgard for 13 months, instead of taking a few months off in winter like the other dogs. He had a light-moderate infestation, he was quite thin and tired easily & had a very poor coat, how much of that was just poor care (he was a chained up backyard dog) and how much the HW, it's hard to tell.

Heartgard does not prevent heartworms, it kills any in the system while they are still at the tiny baby (microfilia? sp) stage and prevents them from growing to the lethal adult size.