Background: The myocardial area at risk (MaR) has been estimated in patients with acute myocardial infarction (AM I) by using ST segment-based electrocardiographic (ECG) methods. As the process from ischemia to infarction progresses, the ST-segment deviation is typically replaced by QRS abnormalities causing a falsely low estimated total MaR if determined by using ST segment-based methods. The purpose of this study was to investigate if consideration of the abnormalities in the QRS complex, in addition to those in the ST segment, provides a more accurate estimated total MaR during anterior AMI than by considering the ST segment alone. Methods: Twenty-five patients with acute anterior ST elevation myocardial infarction (STEMI) received technetium Tc 99m-sestamibi before percutaneous coronary intervention. Single photon emission computed tomography (SPECT) was performed within 2 hours after treatment and was used as a criterion standard for the estimated total MaR. The ECG recorded at admission in the hospital was used for the ECG estimated total MaR. This included an ST-segment estimated ischemic component of the total MaR (Aldrich score) and an estimated infarcted component of the total MaR in the acute phase of AMI by QRS abnormalities (Selvester score). These scores were added for the combined ECG score. Results: The ischemic component of the total MaR estimated by the Aldrich score alone had no statistically significant correlation with SPECT (r = 0.21, P = .32). The infarcted component of the total MaR estimated by the Selvester score showed a significant correlation with SPECT (r = 0.49, P = .01). Each score gave a significant underestimated total MaR measured by SPECT (P <.01). When the Aldrich and Selvester scores were combined, the correlation with SPECT was r = 0.47, P = .02. The combined score still underestimated the total MaR by SPECT (P <.01), though the difference was smaller in comparison to either method alone (P <.01). Conclusion: The ECG estimated total MaR was more accurate by taking both ST deviation and QRS abnormalities into account than by using either method alone. A new ECG method to determine the total MaR during acute coronary occlusion should consider both its ischemic and infarcted components.