"It came out of nowhere," Heaney said. "The pitch before -- a fastball -- didn't come out right, didn't feel like it came out smooth. I didn't think anything of it. [The] release point was a little off, and [my] next pitch was a slider.
"I felt something pull really hard in my lat, and [I] immediately pulled back my arm and it tightened up real bad. It was weird, because I never had any problems with injuries before. It was strange."
While his Class A Jupiter Hammerheads teammates prepared for the upcoming season, Heaney couldn't throw for three weeks. Until the incident, the 6-foot-2, 190-pounder's injury report consisted solely of him once missing the final week of high school baseball after breaking his foot.
"The thing that is really frustrating is, obviously, not playing, but one of the knocks is that I have a tall, slender frame [that is] injury-prone, and I've never been hurt before," Heaney said. "My first full season, I can't even make it out of Spring Training. I want to prove those people wrong.
"Not being able to break with the team and having to watch other people play while you're in rehab is frustrating."
Heaney has started four games since his return on May 20, and recently celebrated his 22nd birthday. In his debut, he allowed one run on four hits over 4 1/3 innings while striking out nine.
In his next outing -- his best so far -- Heaney pitched five scoreless innings, fanning six and walking one. On June 2, he gave up two runs on four hits over just three frames, an appearance Hammerheads manager Andy Haines believes will go a long way toward Heaney's development. And this past Saturday, he went five innings, surrendering just three hits and one run while fanning four.
"We're very encouraged by what we've seen," Haines said. "He's certainly polished. He's not a guy you look at and say, 'He needs to do these two or three things.' All of his pitches are there, his stuff is impressive, very mature."
Three pitches -- all of which he can command -- comprise Heaney's arsenal: a fastball that sits between 90-93 mph and can touch 95, a slider from 82-84 mph and a changeup.
After signing with the Marlins, Heaney landed with the short-season Jamestown Jammers of the Class A New York-Penn League. Two appearances later, Heaney was sent to Class A Greensboro, where he started four games, finishing with a 1-2 record and a 4.95 ERA.
"In player development, you see a lot of guys with Major League pitches, but it takes them a while to learn how to use them," Haines said. "With him, right away you could tell he's got a really good idea of what he wants to do."
Expected to move quickly through the organization, Heaney admitted to playing catchup because of the injury. MLB.com rated Heaney the fourth-best prospect in Miami's organization.
Had he stayed healthy, Heaney thinks he might have been at Double-A Jacksonville by the All-Star break. A Major League callup in September could've been a possibility.
Heaney said it was disheartening to see Minor League guys from big league camp earn trips to the Majors while he battled through his recovery. At the same time, he calls it encouraging for everyone in the organization to see those young players succeed at the highest level.
"I'd love to stay healthy, first off, and reach my innings limit, which I know I'm way behind on," Heaney said. "Moving up would be a goal, obviously, too. I feel like that's a little out of my control. I got a late start, so I don't know how that'll be affected.
"I don't set numbers goals. Numbers can lie sometimes. I just want to go out there and pitch well and try to make up for these two months I missed."