The commissioner's office made the announcement Tuesday, with Heredia's 10-game suspension to be effective at the beginning of the 2006 regular season.
Heredia is the 11th major league player to be suspended for violation of the steroids policy.
The 30-year-old reliever appeared in just three games for the Mets, pitching 2-2/3 scoreless innings following an offseason trade from the New York Yankees.
Heredia was bothered by circulation problems in his pitching hand during the spring and was later diagnosed with an aneurysm in his pitching shoulder, which prompted season-ending surgery.
The veteran has a 28-19 career record with a 4.42 ERA and six saves in 511 career appearances for the Mets, Yankees, Florida Marlins, Chicago Cubs, Toronto Blue Jays and Cincinnati Reds.