Keeping your pet on preventative will stop the microfilarea immutus (baby heartworms) from growing into dirofilarea immuts (adult heartworms). However the already adults will be able to grow in the heart and have the chances to spreading into the lungs depending on how bad the infestation is already. Listen to the vet, they know what they're doing.
Your vet. There are different grades of heartworm disease and obviously your vet feels that your dogs is not bad enough that he has to stop the preventative. It will keep your dog from getting any worse til he can get proper treatment. Basically it will kill the microfilariae (baby heartworms) so no new worms can grow in his heart.
They are both right, in a way. Your vet would be the best to explain this to you. There is more than one kind of medication available to prevent heartworm. I am assuming your vet has advised you on what preventative to use. Have they explained to you what the treatment consists of? Don't put it off any longer than you have to. Depending on how long your dog has had heartworm, you may run into more problems if you wait too long. After the treatment, keep your dog on the preventative, EVERY month, forever. They can get it over and over.
The low dose of the preventative will not cause a massive die-off that would cause issues unless your dog is very heavily infested. Listen to your vet. If you have misgivings, phone your vet and talk to them about why they want you to keep her on the preventative. They will be able to put your mind at ease.
If a dog has light infestation the best way to treat them is by giving them ivermectin (heartguard or iverhart) it will slowly kill the heartworms but it does take time. If your dog has light infestation continue giving the pill once a month and get it rechecked in a year. Coughing is normal and throwing up clear fluid is normal when the worms begin to die off. Bleeding, throwing up blood and bad diarrhea is not normal and you should have them checked immediately. Usually with light infestation there are few problems and your vet was correct in telling you to keep her on preventative. If the infestation is moderate or heavy I would recommend getting the 2 part injections. My rescue dog had to have the 2 part injections and after the treatment is heartworm free and in perfect health. Another dog we came across had light infestation and is on preventative and has a very good prognosis. She will get rechecked in year. Sentinel, Interceptor and other heartworm medications that don't contain ivermection could be very dangerous and maybe that is why your sister was worried. Good Luck with your dog, I hope she is heartworm free in a year!
**Even if you don't have the money and your dog has mod heartworms your vet might suggest just keeping her on preventative, they will eventually die off and she will be healthy again and worm free. Hang in there!
***There is a risk of blood clotting with both forms of treatment.
****The adult heartworms have a short lifespan actually, as you kill the young growth with the pill you stop the cylce, the adult worms die and the problem is solved. I just had a very lenghly meeting with a vet over this.
******the only advantage of the injection (which is 2 part and painful) is that it is definite and faster. With a light infestation the pills do work and in some practices only what is recommended. They do a blood test before prescribing heartworm preventative because they would not prescribe sentinel or interceptor to a HW positive dog and heavy infestation is risky for a slow kill method. Good Luck!
I had heard if dogs have heartworm they should not get the preventative - I mean, that is why they give them the blood test before they give them the preventative in the first place.
Start the treatments and owe the vet - or apply for Care Credit.