"There are three types who deny [kofer] the Torah: 1) One who says the Torah is not from God - even one verse, even one word, if he said that Moshe said it of his own volition [amro mipi atzmo], behold he denies the Torah..."
(Rambam, Hilchot Teshuva 3:8)
"These [the curses in Vayikra 26] are written in plural language and Moshe repeated God's words [mipi hagevurah amran]; while these [the curses in Devarim 28] are written in singular language and Moshe said them of his own volition [mipi atzmo amran]."
(Gemara, Megillah 31b)
Though it is more likely that the Rambam is choosing one gemara (Sanhedrin 79) over another, or else that "mipi atzmo" means different things in Rambam and gemara, the idea that the Rambam considered the gemara to be heresy is slightly amusing. At least to me.