A procedure used to relieve chest pain in hundreds of thousands of heart patients each year is useless for many of them, researchers reported on Wednesday.

Their study focused on the insertion of stents, tiny wire cages, to open blocked arteries. The devices are lifesaving when used to open arteries in patients in the throes of a heart attack.

But they are most often used in patients who have a blocked artery and chest pain that occurs, for example, walking up a hill or going up stairs. Sometimes patients get stents when they have no pain at all, just blockages.

Heart disease is still the leading killer of Americans — 790,000 people have heart attacks each year — and stenting is a mainstay treatment in virtually every hospital. More than 500,000 heart patients worldwide have stents inserted each year to relieve chest pain, according to the researchers. Other estimates are far higher.