Conventionally, if an exercise electrocardiogram does not show evidence of ischemia, the patient must have achieved at least 85% of the predicted maximum heart rate for that test to be considered negative. However, no documentation of the validity of this practice exists. Thus, we evaluated the exercise electrocardiograms of 164 patients who had also undergone coronary angiography within 6 months of the exercise test. The predictive value of a negative exercise electrocardiogram was determined for each percentage point between 50 and 90% of the age-predicted maximum heart rate achieved or exceeded. The predictive value was found to increase modestly between 65 and 80% of the predicted maximum heart rate with no major changes above or below this range. Thus, it appears reasonable (in the setting of a hospital-based exercise laboratory) to either consider a negative exercise electrocardiogram as a valid finding if at least 80% of the predicted maximum heart rate is achieved, or preferably to simply report the negative finding with the percent maximum heart rate attained and the proviso that the predictive value of the test is progressively improved as higher heart rates are attained.