If you've been diagnosed with a clogged artery in your heart, there's a good chance your doctor recommended angioplasty. That procedure involves first clearing out the blockage and then propping the artery open with a tiny cylindrical device called a stent.

More than one million stents are inserted in people in the U.S. to open up blocked coronary arteries every year. Yet researchers have known for nearly a decade that angioplasty usually only saves lives if done immediately after a heart attack.

Here's what you should know about when angioplasty and stents are necessary, and when they aren't.

The Old Thinking

Angioplasty, introduced in the 1980s, gained steam after its effectiveness as an emergency treatment for heart attacks became clear.

In angioplasty, also called percutaneous coronary intervention (PCI), the doctor inflates a thin balloon in the narrowed artery to crush deposits, leaving a stent in place to keep the vessel open.

When performed within hours of a heart attack to clear a blocked or nearly blocked artery, it's clear that angioplasty can be lifesaving.

“Thirty years ago, doctors made the assumption that since it could help with a heart attack, it would help with other blockages due to coronary artery disease,” says David Brown, M.D., a cardiologist and professor of medicine at the Washington University School of Medicine in St. Louis.

When You Do, and Don't, Need It

But a pivotal 2007 clinical trial of 2,287 people with stable heart disease found that having a stent implanted didn’t reduce the risk of death, a heart attack, or other major cardiovascular events when added to a patient’s drug therapy. Subsequent studies had similar results.

Yet 13 percent of nonemergency stents are still inappropriate, according to a Yale University study published online last November by JAMA.

One explanation for the continued use is that the procedure—which is relatively quick and easy—is seen as a moneymaker for doctors and hospitals, says Brown, who has written about the overuse of the procedure.

In most cases, you don’t need a stent unless you’re having a heart attack or have severe angina (chest pain) that doesn’t respond to medical therapy.  

Read more about how to diagnose and treat heart disease and the best drugs for treating high cholesterol.