In 587 patients with acute myocardial infarction (AMI) and no previous MI, electrocardiographically estimated infarct size was related to three-month mortality. Mortality was found to be higher in patients with transmural MI (Q or R-wave changes in standard ECG) than in patients with subendocardial infarction (ST-T wave changes in standard ECG). In patients with anterior MI, precordial mapping with 24 chest electrodes was analyzed four days after arrival in hospital (n = 197). Neither the sum of R-waves, the sum of Q-waves, nor the number of Q-waves correlated significantly with early mortality, although there was a trend towards higher mortality among patients with more pronounced ECG changes. Finally, in patients with inferior AMI (n = 230), neither the sum of R-waves nor the sum of Q-waves in leads II, III and aVF on the fourth day influenced three-month mortality. However, when subtracting the sum of Q-waves from the sum of R-waves, there was a significant correlation between the estimated infarct size and the early mortality.