Don Spencer, a boxing coach at Lord's Gym, in Austin, Texas, could hardly bear to watch DJ Dominguez spar. It was painful. The fledgling amateur boxer got pounded, week in and week out, by more experienced and skilled athletes. But he kept coming back for more, and Spencer knew the teenager had dogged determination. What Dominguez lacked in form and technique, he more than made up in persistence and heart.

And to say Dominguez "has heart" speaks volumes.

Dominguez, 21, is a political science major at the University of Mary Hardin Baylor, in Belton, Texas with aspirations of becoming a professional boxer. But those dreams were crushed during his senior year of high school when doctors told him to curtail all sports and exercise for two to four years because of a tear in his heart. To push the physical limitations, they warned, could lead to further damage and fatal internal bleeding.

They might as well have told him to stop breathing or eating. But Dominguez already had given up eating. That was part of the problem. The lack of nutrition combined with a workout routine that bordered on obsessive caused the damage to his heart.

Looking back, Dominguez could not pinpoint any one event that triggered his behavior. But eating and boxing were the only things in his life he felt he could control.

Just before his first grade year, the Dominguez family - David, Donnas, and son David James - moved from Texas to Minnesota. Like many homeschooled children, Dominguez's social circle consisted of friends from the home school cooperative, church and sports. He became an accomplished swimmer and tried his hands, and feet, at a variety of martial arts disciplines. He had started training in mixed martial arts (MMA) before his family moved back to Texas the summer before his senior year.

Dominguez had a hard time adjusting to his new surroundings. Leaving his friends, enrolling in school - even a private Christian school - and losing the guidance of a respected MMA coach left Dominguez feeling helpless. So he took control of the one thing he could, his body.

His daily routine started well before school each day--sit-ups, running, or boxing.

"Some people have their one cup of coffee," he said. "I had this."

At school, he ran cross country. At home in the evening, he spent another three hours working out. All the while, he ate very little. Food became a reward. When he got a certain skill set perfect in his workout, then he would eat.

The sets were rarely perfect, but he pressed on. His parents took him to a nutritionist, prayed for him and quoted Scripture. But their son still refused to eat, denying his body the essential elements required to repair the muscles he had begun to damage.

During a three-hour workout one unusually hot October evening in 2008, Dominguez "felt something break inside." Chest pains made him think he was having a heart attack. His parents called his doctor and made an appointment for the next morning.

During the exam, the doctor used two different EKG machines. The first one appeared defective. The doctor pulled in a second machine but still could not detect a heartbeat. The nature of Dominguez's injury left him with a heart rate of 20 beats per minute. The normal adult heart rate is 60-100 beats per minute and can be as low as 40 for athletes.

The doctor recommended rest, not surgery, but the real knock-out punch came when he ordered Dominguez not to participate in athletics for up to four years. For a self-described "endorphin freak" that was unacceptable.

"There's no worse feeling than feeling utterly helpless for months on end," he said. "It was infuriating. I had become very, very angry."

The one thing that empowered Dominguez and gave him confidence had been taken away. And he knew it was his fault.

"I hated myself," he said.

Dominguez didn't blame God for his situation because, honestly, he didn't believe in God. He valued his Christian upbringing but "pretty actively doubted."

But during one of his follow-up exams, God challenged his lack of faith.

What physicians believed would be a years-long recovery took just six months. Although perplexed by his healed heart, his doctors confirmed Dominguez could, gradually, begin boxing again. At that moment, Dominguez realized God "actively and radically comes into this world" and works in ways he did not understand.

"I've never doubted the existence of God since then," he said.

But Dominguez admits he's sometimes angry with God. At other times, he questions God's benevolence. Losing fights due to bad judging and watching people he loves suffer and die from cancer weigh heavy on his heart. His coach, Don Spencer, is among those currently battling cancer.

Despite his frustrations, Dominguez knows God has placed certain people in his life.

One of the "God-sends" was Spencer, who does not charge for his coaching services. The car salesman spends his evenings sparring with athletes young enough to be his grandchildren. But the 63-year-old former amateur boxer says teaching keeps him young, even as it keeps him in pain.

Spencer spent most of the last 15 years coaching at Lord's Gym. He has seen aspiring boxers come and go but none have matched Dominguez's drive.

"DJ came into the gym just to spar," he said. "It was really painful to watch him. He was persistent."

Despite the beatings, Dominguez kept getting back in the ring. Spencer saw in him something he hadn't seen in any other contender.

"He is the hardest working athlete I have ever known, hands down," Spencer said. But with Dominguez, hard work must be balanced with good sense. Aware of Dominguez's heart injury and its cause, Spencer pushes his charge as if he were his own son.

"If he needs to be yelled at, I do," he said. "His parents step back. They trust my judgment."

Dominguez also finds a balance between boxing and school. This year he will live at home in Round Rock, between the gym in Austin and the UMHB campus in Belton. The campus and the gym are each about an hour's drive from his house. He also plans to take courses at the Texas State University satellite campus in preparation for taking the LSAT next spring.

As for boxing, Dominguez hopes to turn professional by summer 2013. Although his training ethic can make him appear singularly focused, Dominguez is mindful of what has brought him to this point, and he is grateful.

Parents who support him, a coach who gives freely of his knowledge and encouragement, a sport that demands power tempered with honor, and a God who continues to reveal himself "tells me there's something left to do here," Dominguez said.