Serial ECGs of 16 patients with repetitive attacks of spontaneous angina in the CCU were studied from admission to the hospital to the follow-up phase at the cardiac clinic. Transient repolarization ECG changes occurring during unprovoked angina included ST-segment elevation and ST-segment depression, alterations of T-wave amplitude and polarity, and pseudonormalization of previously inverted T-waves. In addition, QRS complexes were altered transiently during chest pain. Such changes comprised augmentation or reduction of amplitude of R and S waves, widening of QRS complexes and a merging of R waves with the elevated ST-segments. Occasionally the ECG during attacks of angina did not show any change. During asymptomatic periods, between attacks of spontaneous angina, the ECG either returned to baseline, or displayed minor ST-segment shifts, and/or T-wave alterations of varying durations. However, such changes became either persistent or were replaced in the late course of hospitalization by ECG alterations diagnostic of transmural or nontransmural myocardial infarction. Twelve patients suffered an acute myocardial infarction. Four patients died within one month of admission. During follow-up of the 12 surviving patients in the cardiac clinic, amelioration of T-wave changes was noted in the ECGs of patients who remained asymptomatic, but new ischemic alterations were seen in the ECG of patients who had recurrent angina, or were readmitted to the hospital for evaluation. Increase in the amplitude of R-waves, disappearance of Q-waves, or reduction of Q-wave depth were noted at follow-up, in comparison with the discharge ECG, in some patients who had suffered primarily an anterior myocardial infarction.