Medical researchers in Spain say they are close to being able to grow human hearts for transplants outside the body.

Doctors have already grown and transplanted a number of human organs, including windpipes, ears, tear ducts and an artery, The Wall Street Journal reported Friday.

Now, they want to recreate a heart. Researchers in Spain say although the country has the highest number of organ donors in the world, only about 10 percent of patients in need of a new heart get one.

Dr. Francisco Fernandez-Aviles of the Gregorio Maranon hospital in Madrid said that a lab-made version of a heart may be ready in five or six years, and after passing rigorous regulatory and safety hurdles, may be ready for transplant "in about 10 years."

U.S. scientist Doris Taylor, who grew a mouse heart in a lab at the University of Minnesota, says she believes it is possible.

"We opened the door and showed it was possible," she said. "This is no longer science-fiction. It's becoming science."