A heart procedure performed on hundreds of thousands of people a year to relieve chest pain doesn’t work, a new study said.

The research looked at whether the insertion of a stent, a mesh device designed to open a blocked artery, helped patients suffering from angina or chest pain. The condition can be so debilitating that patients can’t even climb stairs.

Doctors insert stents on 500,000 people a year, yet they don’t seem to work, said the study, published in the journal The Lancet.

The study was based on a clinical trial in Britain involving 200 patients with a blocked artery and angina. Other studies have found that stents relieve chest pain but in this one a group of randomly picked patients were made to believe that they underwent a stent procedure when they did not.

The patients were tested on a treadmill to see how long they could exercise and then were put on medication to increase blood flow and prevent a heart attack.

Everyone was wheeled into the operating room and underwent a procedure. Half received a stent. The other half had a catheter inserted and withdrawn in what’s known as a sham procedure.

Six weeks later they were tested on a treadmill. Patients in both groups did better on the treadmill and reported reduced symptoms though patients who received a stent were able to exercise longer. But the difference was not enough to be statistically significant.

Researchers said the results appear to contradict what patients experience after receiving a stent for angina. But they said those improvements are likely caused by the placebo effect.

Dr. Vinay Prasad, an oncologist at Oregon Health & Science University and study specialist, was not surprised by the result.

“Although I have been calling for such a study for years and although I suspected such study would be negative, I’m still saddened to see these negative results,” Prasad said.

“The real lesson here is that costly invasive procedures performed on patients should be tested prior to their use and not two decades later, as in this case.”