Shehecheyanu on pidyon petter chamor

Answer

[1]The Rishonim were divided on whether to recite the blessing of shehecheyanu on the mitzvah of pidyon petter chamor. Some obligated reciting it, comparing it to the redemption of a firstborn human, as the Yire'im wrote (§354): "For it is indeed a commandment to redeem it similarly to a human firstborn." However, the Tur quotes his father, the Rosh, that one should not recite the blessing. Beit Yosef (YD §321) referred to the words of the Tur, saying, "See above in Section 265." His intention was regarding the laws of circumcision, where he cited Rambam's opinion, who stated that one should recite shehecheyanu on the circumcision (Hilchot Berachot 11:9):

Every mitzvah that we are obligated to fulfill infrequently and not found at all times resembles a mitzvah we are obligated to fulfill only at a specific time e.g., circumcising one's son and redeeming him, one should recite the blessing shehecheyanu.

However, the Beit Yosef (YD §265) writes that there are authorities who opposed saying this blessing at the time of circumcision, but he concluded that they nevertheless follow Rambam's opinion: "And in all the Land of Israel and Syria and its surroundings, they say shehecheyanu because they rely on their teachings according to the opinion of Rambam z"l." This is also the ruling of Shulchan Aruch (YD §265:7).

Even though it seems that Beit Yosef's intention in his remark was to compare, based on Rambam's opinion, between circumcision and pidyon petter chamor, and say that one should recite shehechiyanu on both mitzvot. Rabbi Shalom Moshe Chai Gagin noted that while Shulchan Aruch explicitly ruled that one should recite shehecheyanu on circumcision, but did not mention the blessing in the context of pidyon petter chamor. Therefore, it seems that he himself agrees with the opinion of the Rosh that one should not recite the blessing. Aruch Hashulchan (YD §321:15) wrote the rationale for the distinction: "It is not similar to the redemption of a son, which involves joy." However, as we have seen, according to the opinion of Rambam, one should recite shehecheyanu on pidyon petter chamor. Furthermore, there are other criteria for reciting shehecheyanu, such as: fulfilling the commandment for the first time and when feeling joy.

In practice: One should not recite shehecheyanu on the commandment of pidyon petter chamor, but it is a nice custom to wear new clothes or take a new fruit and recite shehecheyanu.