When clots block your heart arteries, you have a heart attack. So it only makes sense that an angioplasty to widen your narrowing arteries before you have a heart attack should prevent it from ever happening and even save your life.

Plenty of patients, and even some heart specialists, still think so. But study after study has been showing that the conventional wisdom is wrong — in most cases, the operation won’t protect you from a future heart attack.

The mounting evidence, along with new treatment guidelines, have been causing a quiet revolution in the treatment of coronary heart disease, shifting patients away from angioplasty in favor of medications, exercise and better diets.

A study published last month in the Journal of the American Medical Association finds that the number of elective angioplasties has fallen by a third in just five years. That mean tens of thousands of people are avoiding a procedure that may have done them little or no good but that costs on average $27,000 and may require years of drug therapy to avoid complications.

Meanwhile, a second new study in the New England Journal of Medicine finds that even after 15 years, patients who chose medication and lifestyle changes over angioplasty were no more likely to die than those who chose the procedure.

“This is a good news story,” said John Spertus, a cardiologist and researcher at St. Luke’s Hospital Mid America Heart Institute and a co-author of both studies. “It’s positive for patients and for society at large that is paying for their care.”

It’s also been a long time coming.

Angioplasty was developed in the late 1970s, a time when doctors thought that heart attacks occurred when cholesterol deposits progressively narrowed coronary arteries, the critical vessels that supply blood to the heart muscle, until they shut off blood flow completely.

During angioplasty, a cardiologist snakes a thin tube, called a catheter, into a coronary artery and then inflates a tiny balloon at the catheter’s tip to push back the deposits on the interior wall of the artery. As the technology advanced, tiny metal mesh tubes called stents were added to the procedure. They’re left in the arteries to keep them open.

Angioplasty has been amazingly successful at relieving the chest pains, called angina, caused by reduced blood flow to coronary arteries. When performed during a heart attack, angioplasty quickly clears blockages to prevent damage to heart muscle and potentially saves lives. That’s made it the gold standard for emergency heart attack treatment.

The popularity of angioplasty grew fast. Eventually, cardiologists were performing 600,000 or more per year. Angioplasty became one of the top 10 contributors to health care costs, according to the Blue Cross Blue Shield Association, racking up expenditures of $10 billion last year.

But from the start, doctors wrongly assumed that the angioplasty done to relieve angina also would make heart attacks less likely by preventing narrowed arteries from closing off entirely.

“I think the faith in angioplasty comes from thinking of the heart as a plumbing problem,” said Cleveland Clinic researcher and physician Michael Rothberg.

It was persuasive, to both physicians and patients, to liken coronary artery disease to kitchen pipes clogging up with fat, Rothberg said. Angioplasty was the drain-cleaning snake that would clear out the blockage and set things right.

But from 1987 to 2007, a dozen or more studies consistently found that while angioplasty could relieve angina in patients with stable heart disease, it didn’t prevent future heart attacks.

As it turns out, most heart attacks occur at places inside arteries where cholesterol deposits appear so mild they wouldn’t be an obvious target for angioplasty. These are deposits that become inflamed and then burst, precipitating a heart attack. This inflammatory model represents current thinking among cardiologists. So now, rather than using plumbing analogies to describe what happens, Rothberg said, doctors should be making comparisons to pimples.

When those “pimples” on artery walls pop, they cause blood in the arteries to clot, he said. If the clot closes off the artery completely, it causes a heart attack.

Even as evidence of the limitations of angioplasty grew, cardiologists kept recommending it, even to patients with mild angina that could be relieved with medication.

“It turns out doctors are people and have all the flaws of humans,” Rothberg said. “They know in an intellectual way that [the studies] are true, but that doesn’t mean they know it in an emotional way. … The fact that they’re paid for [angioplasty] and paid well doesn’t make it easier for them to think the other way.”

And when cardiologists recommend angioplasty, patients have been quick to agree. “It’s scary to have a blockage in your heart,” Rothberg said. “If someone says they can fix it, it sounds like a good idea.”

After 2007, at many hospitals, the practice of angioplasty started to change, and fast, the data from the new Journal of the American Medical Association study show. While the number of procedures done for emergency patients remained stable, elective angioplasties started to plummet, dropping every year from 2011 through 2014. The percentage of angioplasties considered inappropriate was cut in half.

Patrick O’Gara, clinical cardiology director at Brigham and Women’s Hospital in Boston, said, “The field has been evolving in a very positive way. We’re trying to hold ourselves to a higher standard.”