BOSTON -- Andrew Heaney, one of the Angels' most promising young starting pitchers, has relented to season-ending Tommy John surgery, a procedure that will probably keep him out until the start of 2018, the team announced Thursday.
Heaney was hoping to avoid the invasive surgery with stem-cell therapy, which could've had him pitching as early as this September, but his ulnar collateral ligament did not show sufficient progress at the eight-week mark.
Reached by phone, Heaney seemed both disappointed and at peace.
"Once I decided to do stem cell, I knew what I was trying to avoid and what I was trying to repair," he said. "I think I gave it a shot. I gave it every attempt to heal using alternative, conservative methods."
The surgery will be performed by Dr. Neal ElAttrache in Los Angeles on Friday morning. Heaney initially chose stem-cell therapy because he saw Tommy John surgery as a last resort and because he didn't believe he had much to lose since, in his mind, there was a strong chance he would've missed all of next season even if the procedure was done immediately.
Now that surgery is a reality, Angels general manager Billy Eppler said it's "too early" to say whether a return next season is out of the question.
"I don't want to put any timeline on it," Heaney said. "I am not going to limit myself."
Garrett Richards, the Angels' Opening Day starter, is also undergoing stem-cell therapy, but his prognosis seemingly looks better. A Monday ultrasound revealed that Richards is clinically asymptomatic and that his UCL is healing progressively, prompting another evaluation on Aug. 8.
Heaney, 25 days removed from his 25th birthday, was acquired from the Dodgers, shortly after they acquired Heaney from the Marlins, in the December 2014 trade that sent longtime second baseman Howie Kendrick to the Angels' crosstown rivals. Heaney came up from Triple-A the following June and pitched well, finishing with a 3.49 ERA in 105 2/3 innings.
He began 2016 as the Angels' No. 2 starter, and then his arm began to bark.
Heaney felt discomfort in his forearm while completing six innings in his season debut and was promptly placed on the 15-day disabled list with what the team initially called a left flexor muscle strain. He tried to restart his throwing program, but the discomfort ensued. Follow-up MRIs then diagnosed Heaney with a slight UCL tear, with several doctors disagreeing on its severity.

He was told about stem-cell therapy, whereby stem cells are extracted from bone marrow and injected into the affected area to act as a healing agent.
In a message posted on his Twitter account on Thursday night, Heaney called weighing conservative care with surgery "an excruciating decision for me, because I love my teammates, playing the game and competing against the best in the world."

On May 2, Dr. Steven H. Yoon, who operates out of the Kerlan-Jobe Orthopaedic Clinic in Los Angeles, injected stem cells into Heaney's UCL.
On June 13, the six-week mark, Heaney returned for an ultrasound that showed some healing in the ligament, then returned again a couple weeks later.
Heaney was told that patients who have success with the procedure are typically asymptomatic by the eighth week, but that wasn't the case when he showed up to Yoon's office this past Monday. He was told his UCL was not healing at an optimal rate. He tried some strength tests and discovered the same discomfort he was feeling in April. Progress was minimal.
Heaney was due for another follow-up visit shortly after the All-Star break, but ultimately opted against it.
"We felt like we had exhausted all options in terms of giving it more time or re-testing it," Heaney said. "Personally, I guess I thought that I might want to give it time, until the end of the All-Star break. And then the more I started thinking about it, the more I just felt like in my heart that it wasn't progressing at the rate that I had hoped."
Heaney wanted to avoid surgery at all costs, and the Angels supported him -- not just because Richards also has a damaged UCL, or because Tyler Skaggs is 22 months into his own recovery from Tommy John surgery, or because C.J. Wilson has yet to throw a competitive pitch all season.
But because, as Eppler said, "no surgeries are guaranteed."
"Whatever the number is -- 85 percent success rate, 83 percent success rate -- you're still not dealing with certainties," he said. "Opting for conservative care, at that time in the season, did not have a downside associated with it. So I think it was the mindful decision and one that we, together with Andrew, gave our best effort on. It didn't work out that way, but I think we're better for having tried that route."
Eppler spoke to Heaney basically every day over these past couple months. He called him "very levelheaded" and "beyond his years," saying, "I do not feel like I'm talking to a 25-year-old when we speak."
Heaney weighed the conservative-care route pragmatically, and he promises to take the same approach with the arduous rehabilitation that awaits him.
"I don't want to assume anything," Heaney said. "I just want to take it one step at a time. Those little milestones are going to be little celebrations for me. That's how I'm going to stay positive through it."