
Every dog needs to be on medication to prevent heartworms because heartworm disease is a life-threatening disease which is common and potentially fatal. We gladly discuss the pros and cons of each product with you and will help you choose the best one for your pet. We require annual heartworm tests in order to refill heartworm medications. If an animal has microfilaria (lots of immature heartworms) in its blood stream, it can go into anaphylactic shock if given heartworm medication. Also, heartworm medication will not kill heartworms that are more advanced than the microfilarial stage. Dogs that become infected with heartworms despite being on a preventative (e.g. forgetting to give the medication) can develop heart failure.