Gil Heredia made his debut with the San Francisco Giants in 1991, and appeared in 20 games for them from 1991-1992. On August 18, 1992, he was traded to the Montreal Expos in exchange for Brett Jenkins. Heredia played four seasons with Montreal, from 1992-1995. After one season with the Texas Rangers in 1996, he missed the entire 1997 season. He returned to the majors the following year with the Oakland A's. A relief pitcher for most of his career, Heredia did not become a full-time starter until he joined the A's. He pitched a career-high 200.1 innings in 1999 in his first full season with the A's. In 2000, he recorded a career-high 15 wins. He retired after the 2001 season.