Miami Marlins (2012–2014) Minor leagues The
Miami Marlins drafted Heaney in the first round of the
2012 Major League Baseball draft. Heaney was the ninth selection and received an estimated $2.6 million
signing bonus. Heaney began the 2013 season with the
Jupiter Hammerheads of the
High-A Florida State League, and was promoted to the
Jacksonville Suns of the
Double-A Southern League in August. Between Jupiter and Jacksonville, he amassed a 34-inning scoreless streak. Heaney began the 2014 season with Jacksonville, and was promoted to the
New Orleans Zephyrs of the
Triple-A Pacific Coast League in May. In his Triple-A debut, he faced the Oklahoma City Redhawks and went five innings, allowing one run on seven hits while adding seven strikeouts and no walks. He took a no decision.
Major leagues Heaney made his major-league debut on June 19, 2014, against the
New York Mets, going six innings and allowing one run while
striking out three. He took the loss in a 1–0 game. In seven games (five starts) for Miami during his rookie campaign, Heaney posted an 0-3 record and 5.83 ERA with 20 strikeouts across innings pitched.
Los Angeles Angels of Anaheim / Los Angeles Angels (2015–2021) On December 10, 2014, the Marlins traded Heaney to the
Los Angeles Dodgers, along with
Chris Hatcher,
Austin Barnes, and
Enrique Hernández, for
Dan Haren,
Dee Gordon, and
Miguel Rojas. Five hours later, he was traded to the
Los Angeles Angels for
Howie Kendrick. Heaney thanked the Dodgers for their short time together, tweeting, "Well, @Dodgers we had a good run! Great to be a part of such a storied franchise. #thanksforthememories". After some injuries to the starting rotation, Heaney was called up and made 18 starts for the Angels. He went 6-4 with a 3.49 ERA and 78 strikeouts in 105 innings while displaying an excellent strikeout to walk ratio of 2.79 for Anaheim. On June 28, Heaney underwent evaluations on his elbow and found no improvement, pushing back his return even further. On July 1, Heaney underwent
Tommy John surgery and missed the remainder of the 2016 season. Heaney would finish his 2016 season with an ERA of 6.00 in six innings. In 2017, in innings he was 1–2 with a 7.06 ERA and 27 strikeouts. On June 5, 2018, the day of his 27th birthday, Heaney pitched a one-hit complete game shutout as the Angels won 1–0 over the
Kansas City Royals. Heaney was the only Angels starter to start 30 games in 2018. He finished the 2018 season 9–10 with an ERA of 4.15 and 180 strikeouts in 180 innings. On July 6, 2019, Heaney became the first pitcher to start after the passing of fellow left-hander
Tyler Skaggs. His first pitch against
George Springer of
Houston Astros was mimicking an overhand and slow curveball, which was Skaggs' best pitch, and was unchallenged with no swing. In 18 starts, Heaney was 4–6 with a 4.91 ERA. In the 3–7 no-decision loss to the Oakland Athletics, Heaney pitched innings, striking out 6 batters and allowing 1 run. He finished the shortened season with a record of 4–3 in 12 starts. He struck out 70 batters in innings. On August 12, Heaney was the starting pitcher in the first
Field of Dreams game in
Dyersville, Iowa against the Chicago White Sox. Heaney went 5 innings giving up 5 hits, 7 runs, 3 walks, and 3 home runs while striking out 5 batters as the Yankees lost 9–8. Prior to the
2021 American League Wild Card Game, Heaney was
designated for assignment. On October 8, Heaney rejected his outright assignment and elected free agency.
Los Angeles Dodgers (2022) On November 10, 2021, Heaney signed a one-year, $8.5 million contract with the
Los Angeles Dodgers. He made 14 starts and two relief appearances for the Dodgers in 2022, with a 4–4 record and 3.10 ERA while striking out 110 batters.
Texas Rangers (2023–2024) On December 9, 2022, Heaney signed a two-year contract with the
Texas Rangers. On April 10, 2023, Heaney recorded 9 consecutive strikeouts in a game against the
Kansas City Royals, which tied the American League record and set the franchise record. In 34 appearances (28 starts) for the Rangers in 2023, he logged a 10-6 record and 4.15 ERA with 151 strikeouts across innings pitched. In the playoffs, Heaney made three starts. He started Game 1 of the
2023 American League Division Series, and pitched the first innings, a game in which the Rangers went on to win 3-2. In Game 4 of the
2023 American League Championship Series, Heaney lasted only of an inning, surrendering four hits, three earned runs, and one walk. The Rangers would go on to lose the game 10-3. He also started and earned the win in Game 4 of the
2023 World Series, pitching five innings while only allowing four hits, two walks, and one earned run, while also recording three strikeouts. The Rangers ultimately won the World Series in five games, giving Heaney his first
World Series ring. Heaney made 32 appearances (31 starts) for Texas during the 2024 campaign, compiling a 5-14 record and 4.28 ERA with 159 strikeouts across 160 innings pitched.
Pittsburgh Pirates (2025) On February 22, 2025, Heaney signed a one-year, $5.25 million contract with the
Pittsburgh Pirates. Heaney struggled to a 5-10 record and 4.99 ERA over his first 24 games (23 starts), and was shifted to the bullpen on August 16. After continued struggles, including allowing five runs in of an inning against the
St. Louis Cardinals, Heaney was
designated for assignment by the Pirates on August 26. He was released by Pittsburgh on August 29.
Los Angeles Dodgers (2025) On August 31, 2025, Heaney signed a minor league contract to return to the Dodgers organization. In four starts for the Triple-A
Oklahoma City Comets, he recorded an 0.90 ERA with 13 strikeouts across 10 innings pitched. On September 27, the Dodgers selected Heaney's contract, adding him to their active roster. He allowed three runs on four hits in two innings in one game. ==Pitching style==