BACKGROUND: Complex formulas based on elevations of the ST segment on the ECG allow noninvasive estimation of ischemic burden. However, the formulas require elaborate computations that make them clinically useless, particularly in critical and emergent situations. Estimation of the amount of ischemic myocardium is useful in monitoring effects of therapeutic interventions. OBJECTIVE: To compare a simplified formula that sums ST-segment deviations in 12 ECG leads with formulas widely validated in clinical trials: anterior ischemic area = 3[1.5(number of leads ST increases) -0.4]; inferior ischemic area = 3[0.6(sigma ST increases II, III, aVF) +2.0]. METHODS: Data were collected from 46 patients undergoing angioplasty of the left anterior descending branch of the coronary artery or the right coronary artery who had changes in the ST segment denoting ischemia during balloon inflation. Absolute values of ST-segment elevations or depressions in the 12 standard ECG leads with a minimum deviation of 0.5 mm were added to determine the sum of the ST-segment deviations during ischemia of the left anterior descending branch of the coronary artery and ischemia of the right coronary artery. This sum was compared with the anterior and inferior ischemic area scores. The Pearson Product-Moment Correlation Coefficient was used to measure the association between the scores. RESULTS: The sum of ST-segment deviations for the left anterior descending branch correlated with the anterior ischemic area score, and the sum of ST-segment deviations for the right coronary artery correlated with the inferior ischemic area score. CONCLUSIONS: The complex, but validated, formulas for anterior ischemic area and inferior ischemic area correlate well with the simpler sum of ST-segment deviations. Because the simpler sum is more clinically useful, it may provide an alternative for monitoring ischemic burden.