LAS VEGAS – Stefan Struve pushed back the chair and stood up from the computer in his parents' home and felt dizzy. It made him worry for a second, but in the next instant, he dismissed it as one of those things that happens.

He'd been working hard in the gym and, as one of the elite mixed martial arts fighters in the world, was in magnificent physical condition.

But he didn't always feel like he was in great shape.

"I was tired a lot and I'd get home after training without a lot of energy left," Struve said. "I'd fall asleep on the couch. One day, I had a little blackout at my parents' house. That's why I went to the hospital. I was sitting down doing some work on the computer, and when I stood up, I got a little dizzy. Everyone has that now and then, so I wasn't too worried.

"I sat down, and I blacked out for like 15 seconds. That was a little different than just getting dizzy for a split second."

Struve called his trainer and the pair immediately went to the hospital. He did a stress test and on an ultrasound, they found the source of his issues.

In August 2013, Struve was diagnosed with a leaking aortic valve that he said allowed him to compete at only 50 percent of his maximum capacity.

He hasn't fought since being knocked out by Mark Hunt in the third round of a March 3, 2013, bout in Japan. He'll return on Saturday against Matt Mitrione on the main card of UFC 175 at the Mandalay Bay Events Center.

The 6-foot-11 Struve is only 26 and has already compiled a 9-4 record in the UFC. What is remarkable is that he says he did that at such a diminished capacity.

View photos Struve said that before treatment he 'was only at 50 percent heart function.' (Getty Images) More

When he heard he had a heart issue, he was concerned. But in a strange way, he was relieved, because he quickly realized how much he'd been able to accomplish despite his heart issue.

"I did so much in my life as a professional athlete and I was only at 50 percent heart function," he said.

Struve has an enlarged heart and something called a bicuspid aortic valve. The aorta is a cylindrical tube that carries blood from the heart to the rest of the body.

There are normally three valves on the aorta, but Struve was born with just two. As a result, when his heart pumps and sends out blood, not all of it goes out to the rest of the body and some of it leaks back in.

That in essence caused Struve to feel fatigued and not like a guy who'd pushed himself in training to be in peak condition for two months at a time.

Struve said he's eager to return and put on a show against Mitrione. He said despite his UFC success, he hasn't shown how good he can be because he's been limited by his heart.

A UFC spokesman would not make Jeff Davidson, the UFC's doctor, available to speak about Struve or the leaky aortic valve in general and referred questions to the Nevada Athletic Commission.

Struve said he would not fight if he had any concerns and said he has been assured by doctors that he is at no greater risk than any other fighter. His condition has been corrected with medication and he said the result is that he feels better than he ever has going into a bout.

"With the treatments and the pills to lower my blood pressure, they really reduced the size of the left chamber," Struve said. "The left chamber of my heart was bigger than it was supposed to be. Had they not done that, I would have been at risk to develop heart failure.

Story continues