The incidence and significance of pericardial effusions early in acute myocardial infarction remain unclear. Using two-dimensional echocardiography, 172 patients with an acute myocardial infarction were evaluated within 72 h of presentation. Thirty patients (17%) had a pericardial effusion (29 small, 1 moderate) while 142 (83%) did not. No patient developed cardiac tamponade or required pericardiocentesis. Patients with pericardial effusions had higher peak creatine kinase as compared to patients without effusions (2036 +/- 1466 vs. 1483 +/- 1241, p less than 0.05) and a greater number of aneurysms (20% vs. 6%, p less than 0.05). In-hospital mortality was higher in the patients with pericardial effusions (10% vs. 2%, p less than 0.05). In conclusion, pericardial effusions are common in the early AMI period but are generally small and hemodynamically insignificant. They are associated with larger infarcts and greater mortality.