Monitoring the heart with an exercise treadmill, one of the most common tests used to identify people at risk of a heart attack, may not be as effective as previously thought.

The exercise test may fail to predict up to 80 percent of exercise-related heart attacks in apparently healthy men, according to a 10-year study sponsored by the National Institutes of Health in Bethesda .

An exercise treadmill test consists of placing electrodes on the chest while a person runs or walks on a treadmill. A device, known as an electrocardiograph, indicates if the heart is not receiving enough blood when stressed by exercise.

The study was published in the February issue of Archives of Internal Medicine.