The story began in the early 1980s, when researchers discovered a man in the northern Italy village of Limone sul Garda who had very low HDL but no sign of cardiovascular disease. Blood tests revealed about 40 more villagers with the same peculiarity. All traced their origins to a common ancestor born in 1780.

Eventually it was discovered these people carry a slightly unusual version of the main protein that makes up their HDL. Researchers called this ApoA-I Milano and wondered if it might be a supercharged version of HDL. In the first of many animal studies, Shah injected the protein into rabbits with clogged arteries. It quickly cleared them out.

Researchers still argue over whether ApoA-I Milano is a better artery cleaner than the normal version, but it hardly matters. The ordinary kind cannot be patented, so it will never be developed as a drug, but the newly discovered mutant could be. The biotech firm that owns the rights, Esperion Therapeutics, sponsored a pilot study in people.

When the results were released in November, heart specialists were simply astonished. Artery clogging in people takes decades, so many assumed reversing it would be a slow business, too. But after just five weekly infusions, the volunteers' artery buildups had actually regressed about 4 percent. Nothing like this had ever been seen before.

"Many of us didn't believe it would do anything," says Dr. Michael Miller, head of preventive cardiology at the University of Maryland. "The big surprise is that it happened within such a short time. It's unbelievable."

Still, the study was small, involving just 47 patients. Years more testing will be needed to prove the treatment truly safe and effective. Even then, it will have to be given by intravenous infusion, probably making it unrealistic for lifelong use. Instead, doctors envision giving it for a month or two to quickly clean up patients' arteries, a treatment that Esperion head Roger Newton estimates will cost between $2,000 and $4,000.