In our survey, 44 percent of people without heart risk factors or symptoms reported undergoing a heart-specific screening test such as an electrocardiogram, exercise stress test, or ultrasound of the carotid arteries, even though such tests aren't recommended for healthy people.

And most underwent testing without first getting crucial information on the accuracy of the tests, the potential complications, or what they would need to do if the tests came back with worrisome results.

Julia Brown, a registered nurse in Washington, D.C., was one of the exceptions, a healthy survey respondent who opted out of extra testing. "You have to be careful," Brown says. "These shotgun screening tests often lead to additional testing and treatment that has its own dangers. In my line of work, I get to see firsthand the disasters that occur."

A recent study of 2,000 healthy middle-aged adults bears out Brown's experience. It found that people who had a heart scan were more likely than those who didn't to be prescribed medications and to undergo invasive tests and procedures such as angioplasty and even heart bypass. But they are no less likely to have a heart attack or other cardiac event. According to the researchers, those heart scans "do not have a role" in screening low-risk people.

"Once a doctor sees something even remotely abnormal, the reflex is to try to 'fix it' even if there's no evidence that what you saw will cause a problem or that what you are doing will help," Nissen says. He points to a 52-year-old nurse featured in a case study he co-authored in the Archives of Internal Medicine*. False positive results from her heart scan led to unnecessary angioplasty, which set off a cascade of complications and further surgeries, including, finally, a heart transplant.

Proponents sometimes say that the risk of overtreatment is outweighed by the benefit of discovering disease that wouldn't be detected any other way. Not true, our experts say. Standard assessment tools that use information gleaned from basic checkups, such as age, weight, and blood pressure, are good predictors of risk and can help determine effective ways to reduce it. While there are some heart attacks that occur truly without warning, Nissen says it's "rare to have significant narrowing of the arteries and have no symptoms and no other risk factors."

What about the motivational value of picturing the inner workings of your heart? A heart scan does produce "a pretty picture," Lovett says, "but it ultimately doesn't lead to better outcomes."

Paul Ridker, M.D., director of the Center for Cardiovascular Disease Prevention at Brigham and Women's Hospital in Boston, has studied the scans and concluded that they aren't useful for screening. The "deposits cardiologists worry about are the less stable plaques that CT scans routinely miss," Ridker says.

There's one more downside of scans that the ads never talk about: radiation—as much as 200 times the radiation of a standard chest X-ray for some types of CT angiography. Some newer devices use less radiation, but any exposure from an unnecessary test is excessive.