Interruptions During Shema
Question
Can one interrupt shema for any reason?
Answer
Shalom!
Thank you for your question!
It is forbidden to interrupt with any conversation from “Baruch “She’amar” until the end of the service. Furthermore, as a general rule, it is forbidden to respond “amen” or any other prayer response, from “Barchu” until the end of the “Shemoneh Esrei.” But there are some exceptions.
One may answer “amen” (but not “Baruch Hu U’varuch Shemo”) to any blessing when it is “between chapters” of the Shema (or its blessings)
In ancient times, it was permitted to interrupt to greet, or to respond to the greetings, of certain respected individuals, but this is no longer practiced nowadays. One should simply smile or nod if greeting while reciting Shema.
A person is allowed to interrupt by talking in the middle of Shema and its blessings in order to prevent himself from bodily harm or monetary loss, although it is preferable, if possible, to finish the paragraph one is currently reciting.
One is to interrupt the recitation of Shema, even in the middle of a verse, to respond to Kaddish, Kedusha, Barchu, and to bow and say “Modim Anachnu Lach” when the chazzan reaches “Modim.” One who interrupted in the middle of a verse recites that verse from the beginning and then continues.
When responding to Kaddish, one should only answer until “d'amiran b'alma.” One does not answer “amen” to “titkabel,” “yehei shlama,” or “oseh shalom.” This is because these latter responses are customs and later additions. When answering “Amen. Yehei shmei rabba…” one says until the words "le’olam ule’olmei ulmaya".
When interrupting for Kedusha one should only interrupt for the “kadosh…” and “Baruch kevod…” and no more.
One who is called to the Torah for an aliya in the middle of Shema may accept the aliya but he should not read along with the baal koreh as is customary.
In the middle of the first verse of Shema and “Baruch Shem” one should not make any interruptions whatsoever.
The above is normative Ashkenazi practice. Chassidic and Sefardic practice might differ in some of the above.
Source
OC 66:1,3 with commentaries; Mishna Berura 66:2,17,26