[2] In 2008 the Washington Nationals drafted Heston in the 29th round, but he again did not sign and attended East Carolina University.

[2] Heston's professional career got off to a rocky start with a 1–5 record and 4.11 ERA in the rookie Arizona League in 2009.

The Giants clinched a wild card spot with an 88–74 record and eventually won the 2014 World Series, their third championship in five seasons.

[9] Heston was slated to start the 2015 season in AAA Sacramento, but was called up on April 7 to replace the injured Matt Cain.

[11] On May 12, 2015, Heston pitched a complete game against the Houston Astros, allowing only two hits and one run, with 10 strikeouts and no walks.

[12] On June 9, 2015, Heston no-hit the New York Mets 5–0 at Citi Field, becoming the 22nd rookie pitcher since 1900 to throw a no-hitter in a major-league regular-season game.

[14] Heston closed his no-hitter with three strikeouts in the 9th inning, a feat last accomplished by Sandy Koufax in his perfect game in 1965 against the Chicago Cubs.

[14] For his efforts, Heston was honored with his first career National League Player of the Week Award as well as the key to the city by the mayor of Palm Bay, Florida.

[18] Heston was optioned to Triple-A Sacramento on August 21, 2015, to make room for recently acquired outfielder Marlon Byrd.

In 8 games (6 starts) for Rochester, Heston struggled to an 0–3 record and 10.00 ERA with 12 strikeouts across 27 innings of work.