Paul Pendleton played football in college and at age 53, the oil and gas engineer teaches spinning at the Colorado Athletic Club in Denver.

Over the past few years, a knee injury suffered while playing intramural football at age 25 came back to haunt him.

"I was following the ball carrier and stepped in a hole, causing a compression fracture at the top of the tibia," Pendleton recalled.

Surgery removed a fair amount of meniscus, the cartilage that acts as a cushion between the bones. Though it fixed his knee for a time, it also allowed the bones to rub together until he was advised he would likely need a knee replacement.

Knowing how active he is, he was pretty sure he`d blow out a replacement in 18 months. He couldn`t imagine spending six months to rehabilitate a knee he would only ruin again, so he did some Internet research and found Regenexx, a procedure developed by Dr. Christopher J. Centeno that uses patients` adult stem cells to repair damaged tissue.

Doctors at Northwestern Memorial Hospital have successfully treated symptoms of heart disease with their patients' own stem cells as part of a phase-two trial.

The hospital's Feinberg Cardiovascular Research Institute is one of 26 sites across the country participating in the study. The final phase-three trial could begin at the end of this year or early next year, as more sites and patients come onboard.

Heart disease is the leading cause of death in the United States. An American has a coronary attack every 25 seconds, and every minute someone dies from heart disease, according to the Centers for Disease Control and Prevention.

Dr. Douglas Losordo, a cardiologist who heads the research institute, said the phase-two success insures that phase-three is right around the corner. "The phase-two study, from the first patient in till the last patient out, took about two years," Losordo said. "We expect phase-three to be about the same but with more patients at more research sites."