Praecordial mapping of the electrocardiogram (ECG) demonstrated the natural history of ST segment elevation, loss of R and appearance of Q waves in 50 patients suffering uncomplicated anterior myocardial infarction. The results showed that ST segment elevation has a complicated natural history. The loss of R wave electromotive force and development of Q waves were complete by 12 h following the onset of chest pain. This evidence for the loss of viable myocardium was complete before the MB-isoenzyme of creatine kinase (MBCK) was detected in the plasma. Regression analysis of these results showed a direct relationship between the praecordial area of ST segment elevation at 2 h (myocardial ischaemia) and the praecordial area of Q waves at 24 h after the onset of symptoms (cell death). The efficacy of interventions on the natural history of myocardial infarction might be assessed by their effects on the relationship between myocardial ischaemia and cell death.