Yes, but remember to give it on the same date from the next month. Yes, you can give your dog Heartgard two days early as this is a very safe medicine for your dog. Ideally, you should give your dog this Heartgard medicine after 30 days of the first dose.  You can also provide this medicine 30 days after your dog is exposed to mosquitoes. If the treatment is delayed by a few days or many days, then you'll be putting your dog at risk for this condition.