Early career Heinisch started his professional MMA career in 2015 and fought under various promotions, namely Sparta Combat League, and
Legacy Fighting Alliance where he was the interim middleweight champion after defeating Gabriel Checco and was promoted to middleweight champion after
Anthony Hernandez vacated the title in June 2018 when he signed with the UFC. He amassed a record of 10-1 prior to competing in
Dana White's Contender Series. Heinisch was nearly cast for
The Ultimate Fighter: Team Joanna vs. Team Cláudia as a light heavyweight, however, due to paperwork issues from his time in Spain ultimately prevented him from competing. He won the fight via knockout in the first round and was signed by UFC.
Ultimate Fighting Championship Heinisch made his UFC debut on November 17, 2018, against
Cezar Ferreira, replacing injured
Tom Breese at
UFC Fight Night: Magny vs. Ponzinibbio. He won the fight via unanimous decision. His next fight came on May 18, 2019, at
UFC Fight Night: dos Anjos vs. Lee against
Antônio Carlos Júnior He won the fight via unanimous decision. Heinisch faced
Derek Brunson on August 17, 2019, at
UFC 241. He lost the fight via unanimous decision. Heinisch was expected to face
Brad Tavares on October 26, 2019, at
UFC Fight Night 162 However, Heinisch was removed from the pairing in early October for undisclosed reasons. In turn, Tavares was removed from the event entirely and rescheduled to face
Edmen Shahbazyan a week later at
UFC 244. Heinisch faced
Omari Akhmedov on December 14, 2019, at
UFC 245. He lost the fight via unanimous decision. On March 31, 2020, Heinisch revealed that after fighting out his contract, Heinisch signed a new, four-fight contract with the UFC. Finally, Heinisch faced Meerschaert as originally scheduled and won the fight via TKO in the first round. Heinisch was scheduled to face
Brendan Allen on June 27, 2020, at
UFC on ESPN: Poirier vs. Hooker. However, Heinisch pulled out of the matchup in mid-June citing an injury and was replaced by promotional newcomer
Kyle Daukaus. The bout between Heinisch and Allen was rescheduled again on November 7, 2020, at
UFC on ESPN: Santos vs. Teixeira. On the day of the event, the UFC announced the bout was once again canceled due to Heinisch testing positive for
COVID-19. Heinisch was scheduled to face
Kelvin Gastelum on January 30, 2021, at
UFC Fight Night 186. On December 26, 2020, it was announced that the bout had moved to
UFC 258 on February 13, 2021. Heinisch lost the fight via unanimous decision. Heinisch faced
Nassourdine Imavov on July 24, 2021, at
UFC on ESPN: Sandhagen vs. Dillashaw. He lost the fight via technical knockout in round two. Heinisch was scheduled to face
Sam Alvey on February 5, 2022, at
UFC Fight Night 200. Heinisch pulled out due to undisclosed reasons in late December and was replaced by
Phil Hawes. On July 20, 2023, Heinisch announced that he was retiring from MMA to concentrate on treatment for his concussion issues. == Championships and achievements ==