Just for interest, I should also tell you that I do not use flea medication unless I actually see fleas on one of our dogs or on a visiting dog. That has happened twice in ten years in this house and I simply gave the flea medication to them once and that was the end of the fleas. Yes, I inspect them all the time for fleas but the few minutes that takes is far better than filling them full of poison on a regular basis.
I do not give my dogs heartworm medication unless we have a solid week of temperatures staying over 70 degrees (the actual temperature is 70+ and the length of time is closer to 10 days, but I err on the side of caution). It's very, very rare that we have temperatures over 70 during the night time hours here in Baltimore. At any point in the development of heartworm larvae in a mosquito, if the temperature drops below 70 degrees that is the end of the larvae. It can go up to 100 the next day but the larvae does not resurrect itself. In 17 years none of my dogs have been positive for heartworm and we lived on a 150 acre farm for five of those years where the dogs were walked in the woods on a daily basis. (Gee, sure miss that farm) The area around us is full of poison ivy and while it won't hurt the dogs they can carry the oils back to humans unless it's washed off after every walk. I'm not willing to do that so I stick to walk on pavement.
