HPI: A 22 year-old male presented to the emergency department with a chief complaint of retrosternal chest pain that started yesterday. He described the pain as a constant, sharp and pleuritic. The pain was worsened by lying flat, and improves with leaning forward. He reported having a sore throat and other cold symptoms earlier in the week. The patient’s exam was notable for a faint pericardial friction rub. A bedside echocardiogram demonstrated normal cardiac function without pericardial effusion. The patient’s ECG is shown. Significant findings: The ECG shows diffuse ST- elevation. The patient also has mild PR-depression, most notably in the inferior and lateral leads. The patient also has minimal PR elevation in lead aVR. The patient was diagnosed with acute pericarditis (ECG stage 1). Discussion: Pericarditis is inflammation or infection of the pericardial sac. There most common etiologies are viral or idiopathic1,2. While it is rarely fatal, acute pericarditis can cause severe, disabling pain2. Furthermore, concomitant myocarditis can cause significant morbidity and mortality. Classic ECG findings include diffuse ST-elevations and PR- segment depression, without reciprocal ST-segment depression (as shown in this image). The ECG of pericarditis may move through various stages when followed over time1,2. These include stage 1: diffuse ST-elevations with concave-upwards contour, PR- depressions (most common in II, aVF, V4-6); stage 2: ST segments become isoelectric and T waves flatten; stage 3: symmetric T wave inversion throughout ECG; and stage 4: ECG normalization2. These ECG changes have variable sensitivity and specificity depending on the stage, with less than 50% of patients progressing through the classic stages2.