Mike Fackelmann had no reason to think he had heart disease. Although his cholesterol was a touch on the high side, he had never experienced any chest pains and had just passed a stress test with flying colors. when a cardiologist at the Cleveland Clinic Foundation Hospital asked the then 49-year-old registered nurse to help demonstrate an experimental new cardiac scanner, neither the physician nor Fackelmann expected to see anything out of the ordinary. The idea was simply to slide Fackelmann through the machine and show what finely detailed images of the heart it could produce.

The favor Fackelmann did may well have saved his life. The scan revealed a major blockage in one of his coronary arteries. A few days later, doctors propped open the dangerously clogged blood vessel with a stent, thereby preventing what could have been a heart attack. “I would have been one of those guys who was just out jogging with my son or playing basketball and died,” Fackelmann says. “There was never any reason for me to suspect that there was such a dramatic lesion in my heart.”

What makes this story all the more remarkable is that the image that changed Fackelmann’s future was generated without any kind of surgery. For years, the gold standard for discovering the location of blockages in a patient’s coronary arteries has been a procedure called a cardiac catheterization, in which a specialist inserts a probe through an incision into a blood vessel in the groin, then snakes it up toward the heart, where an opaque dye is released.

Any lesions or plaques that block the arteries then show up on an X-ray picture called an angiogram. And if you don’t consider catheterization real surgery, you don’t understand how invasive and delicate an operation it actually is. The process can take anywhere from four to six hours and carries a 1% risk of serious complications, including death, from wayward catheters that can tear the delicate artery walls–which is why doctors don’t order it lightly. Yet 20% to 40% of patients who take the risk turn out not to have needed it: they show no significant blockages in their arteries.

Or at least that’s where things stood until recently. The past 18 months have brought a wave of advances in cardiac imaging, leading many doctors to wonder whether it’s time to change the way they diagnose and treat heart disease. Leading the way are improvements in CT (for computed tomography) scanning, which uses highly specialized X-ray machines to take multiple, finely layered pictures of the heart and surrounding blood vessels. Sophisticated computer programs sort the data to generate amazingly detailed, three-dimensional images like the ones that alerted Fackelmann’s doctors to his hidden heart problem. Advances in other techniques like MRI (magnetic resonance imaging) have astonished physicians with the clarity of details now available to them on the inner workings of the heart.

What that means is that millions of patients will probably get the treatment that better matches their condition. Some doctors are already starting to use the scans to figure out which of their otherwise healthy-seeming patients need to be taking cholesterol-lowering drugs like statins, and may even be able to decide what to do in marginal cases without having to resort to an invasive angiogram. Patients with a clean scan, on the other hand, can feel confident that they don’t need statins or other medication, along with their potential side effects.

The most dramatic benefits of the heart-imaging revolution will probably show up first in emergency rooms. About 5.5 million people go to the hospital each year complaining of chest pain. Most of them are not suffering a heart attack, but it can be very tricky to separate out which ones have indigestion or a strained muscle from those who have something much, much more dangerous. A noninvasive test that shows whether or not the cardiac blood vessels are blocked could help make the diagnosis a lot easier. “We used to say to patients who came in with chest pain ‘I don’t think you have coronary disease,’” says Dr. Mario Garcia at the Cleveland Clinic, which has been one of the early adopters of cardiac CT scans. “Now I can tell them, ‘I know you don’t have coronary disease.’ That’s a big difference.”

Medical groups are racing to keep up with these changes. In July, the American College of Cardiology and the American Heart Association published their first guidelines on how to train doctors to perform the new cardiac scans. Three studies have shown that cardiac CT is 90% accurate at picking up blockages like Fackelmann’s. But no standards have been written yet for determining under what conditions using the new scans makes the most sense, and for which patients. More definitive answers may be forthcoming at the annual American Heart Association meeting in November, when several research groups are expected to present their latest studies.

The technological boom has come so fast that doctors and patients are faced with the challenge of sorting the scans from the scams. Medicare and insurance companies are looking with growing alarm at the overall surge in the use of expensive imaging scans for all parts of the body. The reasons for the increase are complex–and hotly disputed–but many cardiologists are worried that fights over which procedures get reimbursed and who gets to order them could strangle the latest innovations.