Heartgard Plus is given once a month year round for the prevention of heartworm disease. The usual dose of heartgard plus in dogs up to 25 pounds is 68mcg/57mg, for 26-50 pounds is 136mcg/114mg and for 51-100 pounds is 272mcg/227mg. Dogs over 100 pounds are given a combination of tablets. As an alternate to year round dosing, this medication can be given during the mosquito season and for one month after the season ends.