Q. If someone is overly careful to pronounce the words of the shema properly and keeps on repeating them many times, trying to get it just right, is that not a hefsek?
Thank you

A. Horav Shlomo Miller’s Shlit”a opinion is that it should certainly be avoided. One should train himself to recite the words properly and with the correct grammatical expression the first time. Additionally, it may occur that when repeating the word several times, in the end only part of the word will be recited properly or not at all, resulting in the non-compliance of the mitzvah.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a