Recently two types of atypical T-wave evolution were recognized as electrocardiographic (ECG) markers of regional postinfarction pericarditis. The sensitivity and specificity of these changes for this condition were 100 and 77%, respectively. The major purpose of this investigation is to show how these ECG changes can be used to differentiate among postinfarction pericarditis, postinfarction angina, and reinfarction. Even appropriately constructed serial monitor lead ECGs can be used to make this distinction. The ease of correctly distinguishing among the three causes of postinfarction chest pain utilizing a carefully elicited history and ECG criteria is discussed. In addition, a secondary objective was to assess the effect of lytic therapy on the incidence of postinfarction pericarditis. Among the 200 patients in this study, lytic therapy halved the incidence of postinfarction pericarditis, which is in accord with the larger Gruppo Italiano per lo Studio della Streptochinasi nell'Infarto Miocardico (GISSI) study.