Heston won ERA titles in 2011 with Class A San Jose and last year with Double-A Richmond while posting an aggregate 21-12 record. He displayed admirable command during that span, striking out 266 and walking 80. This year, however, Heston has struggled with Triple-A Fresno, posting a 7-6 record with a 5.80 ERA, 97 strikeouts and 46 walks in 108 2/3 innings. His WHIP is an inflated 1.61.
When the Giants needed to summon a starter from the Minors to replace injured right-hander Ryan Vogelsong, they selected left-hander Mike Kickham, not Heston.
A closer look at the non-Major Leaguers on the 40-man roster indicated that Heston was the most logical choice to place in limbo -- players designated for assignment have 10 days to wait for a trade, be released, or clear waivers to sign as a free agent.
"That's a good problem to have," Giants vice president and assistant general manager Bobby Evans said. "You don't have easy choices."
Shortstop Ehire Adrianza possesses above-average defensive skills. Left-hander Edwin Escobar is one of the organization's fastest-rising prospects. First baseman Angel Villalona wields impressive power. First baseman Brett Pill continues to crush the ball for Fresno (.345, 14 homers, 68 RBIs in 58 games).
The Giants also optioned right-hander Jean Machi and infielder Nick Noonan to Fresno, lengthening their season-long series of round trips between San Francisco and Fresno.
Chris Haft is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.