Pericardial effusion after myocardial infarction is a relatively common, however the management and prognosis is not always straightforward. Regardless of effusion size, data suggests that pericardial effusion which occurs early post myocardial infarction were correlated with higher morbidity and mortality. This report describes a case of pericardial effusion occurrence after myocardial infarction and reviews published literature about the etiology and management of this complication. A 59 years old man with typical chest pain since 26 hours before refered to emergency room, sign and symptoms of cardiogenic shock, elevated cardiac marker, and electrocardiogram showing ST elevation in V1-V6, I, aVL (extensive anterior). He was observed and conservatively treated in intensive cardiology care unit. After 9 days of care, moderate pericardial effusion is revealed by echocardiography examination, which did not exist at the admission. Pericardial effusion (PE) as the complication of myocardial infarction is associated with anterior ST-segment elevation myocardial infarction (STEMI) and when there is heart failure. Poor ST-segment resolution is clearly associated with presence of PE and especially with tamponade or electromechanical dissociation. The most frequent cause of moderate PE in STEMI patients is bleeding from the infarcted wall. STEMI patients with a moderate PE have increased mortality than those with small PE or without PE, and death was attributable to free wall rupture (FWR). It is necessary to detect PE earlier with echocardiography and some deserve close monitoring to detect FWR.