I just adopted a dog from Ohio. The health record I recieved with him says he was tested for heartworm in Ohio and it was negative. The test was done the middle of June. I didn't aquire the dog until a month later. He wasn't on any type of preventative in that period of a month. I took him to my vet 1 1/2 weeks ago, right after I aquired him. I asked the vet if he should be tested again and he didn't think so. He gave me sentinal for the dog and started him the same day. He told me to give him his second pill today. Is that too soon, or should I wait the recommended 30 days? Can he overdose on Sentinal if given too soon? Has anyone done this with their dog before?