141:11 The one who reads the Megillah recites three brachos beforehand, both by day and by night. He recites “al mikra megillah” (that G-d commanded us regarding reading the Megillah), “she’asa nissim” (that G-d performed miracles for our ancestors), and “shehechiyanu,” (that G-d sustained us to reach this occasion). After reading the Megillah, he rolls it up, lays it down in front of himself, and recites the bracha “harav es riveinu” (that G-d fights for us). If a mourner reads the Megillah, someone else should recite the brachos because a mourner is not supposed to recite shehechiyanu in public.
141:12 When reciting the bracha of shehechiyanu by day, one should have in mind also the mitzvos to send portions of food to one another, to give gifts to the poor, and to have a special Purim meal. The one reading the Megillah must likewise intend to include the others also for these three mitzvos. (There is a question as to whether or not one without a Megillah should recite shehechiyanu for the other mitzvos of the day; if he heard shehechiyanu at night, he certainly should not – Mishnah Brurah 692:1.)