Background: The ability of the 12-lead electrocardiogram(ECG)to quantify size and transmural extent of myocardial infarction(MI)is not fully explored. Q wave s are still thought of as indicative of transmural MI despite that several studies have rejected this association. We hypothesized that size and transmural extent of acute MI indeed can be estimated by QRS scoring on the 12-lead ECG using delayed, contrast-enhanced magnetic resonance imaging(DE-MRI)as gold standard and that Q waves are not predictive of transmural MI. Methods: Twenty-nine patients with first-time reperfused MI were studied. Delayed, contrast-enhanced magnetic resonance imaging was performed and 12-lead ECG was recorded 8±1 days after the acute event. Myocardial infarction size and transmurality were determin ed by DE-MRI and compared with Selvester QRS score from the ECG recorded on the same day. Results: There was a good correlation(r=0.79, P< .001)between MI size by QRS scoring and DE-MRI.As local MI transmurality increased as assessed by DE-MRI, the local QRS score increased progressively(P< .001). There was no significant difference in the number of Q-wave-related QRS points between nontransmural and transmural MI(1.8±0.6 vs 2.9±0.4, P=.14). The global QRS score, however, differed significantly(3.1±0.8 vs 5.1±0.6, P< .05). Conclusion: QRS score is significantly related to both MI size and transmurality by DE-MRI in patients with first-time reperfused MI. Presence of Q waves, however, is not indicative of transmural MI in these patients. Thus, QRS scoring could potentially be used for diagnosing and characterizing MI in patients with suspected recent MI. Background: The ability of the 12-lead electrocardiogram (ECG) to quantify size and transmural extent of myocardial infarction (MI) is not fully explored. Q wave s are still thought of as transmural MI despite that several studies have rejected this association We hypothesized that size and transmural extent of acute MI indeed can be estimated by QRS scoring on the 12-lead ECG using delayed, contrast-enhanced magnetic resonance imaging (DE-MRI) as gold standard and that Q waves are not predictive of transmural MI. Methods: Twenty-nine patients with first-time reperfused MI were studied. Delayed, contrast-enhanced magnetic resonance imaging was performed and 12-lead ECG was recorded 8 ± 1 days after the acute event. Myocardial infarction size and transmurality were determin ed by DE-MRI and compared with Selvester QRS score from the ECG recorded on the same day. Results: There was a good correlation (r = 0.79, P <.001) between MI size by QRS scoring and DE-MRI.As local MI transmural There was no significant difference in the number of Q-wave-related QRS points between non-transmural and transmural MI (1.8 ± 0.6 vs 2.9 ± 0.4, P = .14). The global QRS score, however, differed significantly (3.1 ± 0.8 vs 5.1 ± 0.6, P <.05). Conclusion: QRS score was significantly related to both MI size and transmurality by DE- MRI in Patients with first-time reperfused MI. Presence of Q waves, however, is not indicative of transmural MI in these patients. Thus, QRS scoring could be used for diagnosing and characterizing MI in patients with suspected recent MI.