Stress tests don't always predict heart attacks.

Stress tests don't always predict heart attacks.(SEAN JUSTICE/CORBIS)

Your doctor can't tell how well your heart is working until it's put to the test. If you have heart disease—or if you're at risk—your doctor may want to examine your heart during exercise. The stress test can spot hidden problems with your heart and help determine how much exercise you can safely handle.

Kit Cassak, 63, of Scottsdale, Ariz., had had a regular electrocardiogram (ECG or EKG) test in the past, but when she experienced shortness of breath and chest, arm, and jaw pain during physical activity, her doctor referred her to a cardiologist for a stress test. "They hooked up these different electrodes pretty much like an ECG, and they got me to walk on this treadmill, which I'd done during my normal workouts. In less than two minutes they started to see something on their screens and I told them I was feeling symptoms," she says. The cardiologist immediately stopped the test and referred her to the hospital for an angiogram to look for blockages in her blood vessels. The test determined that she needed open-heart surgery.

Who should have a stress test?
Stress tests may be particularly effective for women. Because they don't use radiation, they can be safely used for women who may be pregnant. A recent study by researchers at St. Luke's–Roosevelt Hospital Center in New York City found that stress echocardiograms—a pair of echocardiograms administered before and after exercise—were highly effective in stratifying women into high-risk and low-risk groups for coronary artery disease.

Doctors may also order stress tests after patients have recovered from a heart attack or heart surgery. Mark Miller, 62, of Linden, Calif., put off surgery after having two heart attacks five years ago, but when he failed his fourth stress test, he realized he couldn't wait any longer. "I couldn't go more than one and a half minutes on the treadmill, and the last one, I just collapsed on it," says Miller. Eight months after his heart attack, Miller agreed to have heart surgery. Today he works hard to keep fit and takes an annual stress test. "The last time I went, I lasted for 15 minutes and could have gone longer," he says.

Doctors may also take pictures of your heart
Doctors may also take pictures of your heart before and after exercising by performing a nuclear stress test. "You use an imaging agent, inject it into the patient, and then they go under the camera before and after you put them on the treadmill," explains Jennifer Mieres, MD, director of nuclear cardiology at the New York University School of Medicine. If a patient has blockage of the blood flow to the heart or if they've had a heart attack in the past, it will show up," says Mieres. Nuclear stress tests are 90% accurate, compared with exercise stress tests, which are about 75% accurate for men and just over 60% accurate for women. When it's appropriate, Mieres prefers to use nuclear stress tests for women.

If you're unable to exercise, doctors may perform other tests including some that simulate how the heart responds to exercise.