The Gemara in Masechet Berachot cites a ruling of Rabbi Yehuda that one should not make any interruptions in between the end of Shema and the first word of the Beracha recited after Shema. After one completes the Shema recitation with the words, "Ani Hashem Elokechem," he may not make any interruption before reciting the word "Emet" with which the next Beracha – "Emet Ve’yassiv" – begins. There are points during the Shema recitation where one may interrupt under certain circumstances for the purposes of extending a greeting or replying to a greeting; in between "Ani Hashem Elokechem" and "Emet," however, one should not interrupt for any purpose. The Gemara bases this ruling upon a verse in the Book of Yirmiyahu (10:10), "V’Hashem Elokim Emet." Just as Yirmiyahu declared "Hashem Elokim Emet" in a single phrase, we, too, should recite "Hashem Elokechem Emet" without interrupting in between "Elokechem" and "Emet."
The Halachic authorities debate the question of whether this Halacha applies to silent interruptions. It occasionally happens that a person recites Shema ahead of the Hazan, and completes the recitation well before the Hazan. If he waits silently after completing "Ani Hashem Elokechem" so that he could recite "Emet" together with the congregation, he will be making a long, silent pause in between "Ani Hashem Elokechem" and "Emet." Does this violate the Halacha mentioned in the Gemara, or does that Halacha refer only to verbal interruptions?
The Kaf Ha’haim (Rav Yaakov Haim Sofer, Baghdad-Israel, 1870-1939) ruled (61:12) that the Gemara forbids only verbal interruptions, and one may therefore make a silent pause in between "Ani Hashem Elokechem" and "Emet" as he waits for the Hazan to complete Shema. Several other authorities, however, including the Mishna Berura (Rav Yisrael Meir Kagan, 1839-1933), the Hesed La’alafim (Rabbi Eliezer Papo, 1770-1828) and Hacham David Yosef (in his Halacha Berura), rule stringently in this regard. In their view, it is forbidden to make even silent interruptions in between the end of Shema and the beginning of "Emet Ve’yasiv." There are sources among the Rishonim (Medieval Halachic scholars) that appear to prove this position, and this is, indeed, the view that one should follow. Therefore, if a person recites Shema ahead of the Hazan, he should wait for the Hazan before the beginning of the final verse of Shema – "Ani Hashem Elokechem Asher Hoseti Etchem…" and then recite that verse together with the Hazan and the congregation. He should not recite that verse independently and then pause after completing "Ani Hashem Elokechem."
Summary: One should not make any verbal or silent interruptions in between the end of the Shema ("Ani Hashem Elokechem") and the word "Emet" which introduces the Beracha recited after Shema. Somebody who recites Shema ahead of the Hazan should wait before beginning the final verse of Shema ("Ani Hashem Elokechem Asher…") and then complete Shema together with the congregation.
