WASHINGTON (AP) -- The government is beginning a $30 million study to determine once and for all whether chelation therapy offers any benefit for sufferers of heart disease.

Chelation therapy is the main treatment for lead poisoning. A manmade amino acid called EDTA is seeped into patients' blood, through a vein, to sop up the toxic metal so it can be excreted in urine.

Some doctors have argued for decades that chelation therapy also could clear blocked heart arteries, perhaps by sopping up inflammation-causing molecules or calcium in buildups that clog blood vessels.

No one has ever proved chelation truly helps the heart. The first rigorously controlled clinical trial found last year that chelation failed to relieve heart disease.

Federal regulators have cracked down on proponents for falsely promoting chelation as a proven heart remedy -- several years ago the Federal Trade Commission forced a doctor's group to quit such advertising -- and warned that the therapy can cause kidney damage or other side effects, especially if not administered by a properly trained professional.

Last year's clinical trial was small, however, and proponents counter with numerous reports of patients who say chelation relieved their chest pain. Americans spend millions of dollars each year on chelation, either in addition to standard treatments like cholesterol-lowering drugs or as an alternative.

So the National Institutes of Health's alternative medicine center decided to fund a big enough experiment -- involving 2,372 heart-attack survivors -- to possibly settle the debate. Led by Dr. Gervasio Lamas of the Mount Sinai Medical Center-Miami Heart Institute, the five-year study will begin enrolling participants at about 100 different spots around the country in March.

Participants will receive 40 intravenous infusions, each lasting three to four hours, under methods endorsed by the American College for Advancement in Medicine, a doctors group that promotes the treatment.

Half the participants will have chelation drugs dripped into their veins; the other half will get a dummy intravenous solution. Scientists will track whether chelation recipients live longer, suffer fewer heart attacks or strokes, need less hospitalization for chest pain and need fewer angioplasties or bypass surgeries.

Study participants will get standard heart treatments, so the question is whether chelation will provide any added benefit.

Lamas said he decided to design the study when one of his own patients asked about chelation.

"While my answer, as a very conventional cardiologist, was initially, 'No, that's silly,' as I looked into it I realized I didn't really have the evidence base to say that," Lamas said. "Now we'll see what the real truth is."

Indeed, Lamas said, the need for a rigorous chelation study was reinforced last month when the NIH abruptly stopped a study of hormone replacement therapy that found -- to many doctors' shock _ that long-term use harmed instead of helped women's health.

The chelation study is "really important," agreed Dr. Rose Marie Robertson, former president of the American Heart Association. "If it's a positive study, that will be wonderful, and if it's not then we can in a definitive way tell people not to use this."

The heart association has long cautioned patients not to try chelation in place of proven heart treatments. Patients now considering chelation should "wait for the results of this trial," Robertson advised -- or enter the study instead of seeking chelation elsewhere.

To enroll in the NIH-funded study, patients must be heart-attack survivors age 50 or older who have never undergone chelation therapy, don't smoke and haven't undergone an angioplasty or bypass surgery or have one planned within the next six months