Two Heartbeats: Kabuto's Trap

is episode 140 of the original Naruto anime.

Synopsis
Naruto arrived in the nick of time to save Sakura, but not before Kabuto told her that Sasuke was dead. Naruto told her not to believe him, after which a battle ensued. Naruto managed to defeat him with the Rasengan, but Kabuto trapped him with some chakra threads that connected their hearts; if Kabuto's stopped, so would Naruto's. As Kabuto attempted to kill himself in order to end Naruto's life, Sakura tried to free him. Sasame arrived and gave Sakura a special Fuma clan tag to help save Naruto, only to find out that the Kabuto they had fought was actually Kagero, who died after suggesting that Sasame should not know what Arashi had become. They finally found Arashi, who had been disguised as Orochimaru, who revealed that he had indeed changed.