Niese later told reporters it was the first time since 2012 that his had a rapid heart rate while pitching.
According to Niese, he has only experienced the rapid heartbeat on field and that he does not take medication for it.
"If it happened on a more regular basis, I'd probably do something about it," Niese said.
He gave up three hits, struck out four and did not allow a run in 5 1/3 innings in his final start of the season.
Niese will finish the season 9-11 with a 3.40 ERA.