Background: Repolarization ECG changes during an episode of pain in patients with suspected unstable angina (UA) or non-Q myocardial infarction (N-Q MI) are considered as very specific for myocardial ischemia. However, its prognostic value was not prospectively studied in large series of patientsMethods: The prognostic value of ischemic ECG changes obtained during the first observed episode of pain as compared to the ECG without pain was prospectively evaluated in 1899 consecutive patients considered to have UA or N-Q MI when first seen by a cardiologist at 18 centers in Spain.Results: Mortality at 90 days follow-up was higher when ST segment depression =<0.1 mV was observed during pain and lowest when both ECG (with and without pain) were normal. The figure shows the Kaplan-Meyer survival curves for the different groups.Conclusion: Downward shift of ST during pain is the variable related with highest mortality in patients with suspected UA.