It is expected to be during the season because of depth in front of him in the organization. For now, Heaney is going along for the ride, striving to do his part on the mound and let the front office and coaching staff decide his next step.
"I want to stay here as long as possible," Heaney said. "I want to get innings, and I understand once the innings run out, they've got to give it to the guys who are going to be there to start the season."
Heaney has been given 7 2/3 innings in Grapefruit League play, and he has a 2.35 ERA, with four strikeouts and a WHIP of 0.91.
On Thursday against the Tigers in Lakeland, Fla., the lety threw three scoreless innings.
"I feel every time out I've gotten better," Heaney said. "I felt against the Tigers, it was the best my stuff has been this spring. My mechanics felt good. I was hitting spots."
Heaney, 22, will open the season at Double-A Jacksonville, where he finished 2013.
The Marlins have not historically started off their top pitching prospect at Triple-A, but their Double-A rotation is pretty deep with Justin Nicolino, Anthony DeSclafani, Jose Urena and Angel Sanchez expected to anchor four spots.
Every day Heaney is in camp, he feels more like he belongs. And facing great hitters like Detroit's Miguel Cabrera helps him gauge where he's at in his development.
"It's kind of a self-confidence thing to know, they're really good, they can hit, but I can pitch," Heaney said. "I can hold my own. To prove that to myself is good."
Joe Frisaro is a reporter for MLB.com. He writes a blog, called The Fish Pond. Follow him on Twitter