“Your doctor” may be wrong in doing so, though, according to a controversial study published last week that, if widely accepted, has the potential to change the course of medicine. Data in The Lancet showed that among people with severe blockage of the coronary arteries, the procedure did not improve angina—the reason for nearly 500,000 PCI procedures worldwide every year—or ability to exercise on a treadmill. Now after 40 years, millions of procedures, and billions of dollars, doctors are questioning whether the common procedure is, in most nonemergency cases, doing much less good than previously believed, if any.

But many patients and doctors swear it works. Mandrola describes a typical case: A patient is told they should have this cardiac catheterization because of chest pain and a cardiac-stress test that suggests disease. Patients come to understand from friends and the internet that if a blockage is found, the doctor will “fix it.”

“Blockages are deadly and must be fixed, goes the thinking,” Mandrola explained. “So they do the PCI, and they bring the family into the lab or show them pictures of the blockage. Everyone is happy. Doctors, nurses, patient, and family. That whole scenario creates a whirl of placebo effect. And the patient feels better.”

“I’ve been saying for many years that we don’t know if patients feel better from stents, or if they feel better because patients always feel better when we do an invasive procedure,” said Rita Redberg, a professor of medicine at the University of California, San Francisco. “That’s how the mind words.”

Knowing that this procedure’s effect is based heavily in placebo, it would seem, will diminish its effect. Reading this article may cause people to have more chest pain.

If stents to open clogged coronary arteries indeed don’t help people in nonemergency situations, this would be among the highest-stakes disappointments in medicine to date, when more than anything else, people around the world die of heart disease. It usually involves blood vessels getting progressively clogged up and then totally blocked. This causes the heart muscle to die, and so the person dies.

“This is a hugely disruptive study,” said Mandrola. “The implications are huge. Billions of dollars have been spent, and many hundreds of thousands of patients have been exposed to the risks of PCI, without any documented benefit.”

Redberg went even further. “I think this has shown definitively that there was no benefit on exercise time, no benefit for angina, no benefit for functional status—it was pretty definitively negative.”

So are there any reasons—outside of an acute heart attack—to do PCI?

“I can’t think of one,” she said. “Why have a person undergo the risk of the procedure?”

Mayo Clinic makes these risks clear: The abridged version includes blood clots, heart attack (the wire can displace some of the plaque inside the wall of the artery and actually cause a heart attack), coronary-artery damage (recall that there is a wire and force-inducing balloon being inserted into the three-millimeter vessels on the surface of the heart), abnormal heart rhythms, kidney failure, and stroke. These are rare outcomes, but they become increasingly relevant as the benefits of the procedure become less clear.