Diffuse ST elevation (concave upward) usually present in all leads except aVR and V₁; PR-segment depression (and/or PR elevation in lead aVR) may be present; days later (unlike acute MI), ST returns to baseline and T-wave inversion develops (See Table 116-2 and Fig. 116-1). Atrial premature beats and atrial fibrillation may appear. Differentiate from ECG of early repolarization (ER) (ratio of ST elevation/T wave height <0.25 in ER, but >0.25 in pericarditis).