The association between recent atrial fibrillation during the course of acute 
myocardial infarction and pericarditis or pericardial effusion occurring during 
the hospital phase of myocardial infarction was studied by means of serial 
echocardiographic examinations in 192 patients presenting with their first 
myocardial infarction. Clinical pericarditis was found in 8%, echocardiographic 
effusion in 43%, and atrial fibrillation in 5% of all patients. Atrial 
fibrillation was present in only 2% of patients without pericardial effusion 
compared to 15% of patients with more than minimal effusion (p = 0.0094). Thus, 
pericarditis might play a role in the development of recent atrial fibrillation 
during the course of myocardial infarction. Recent atrial fibrillation may be a 
sign of pericardial effusion which may be otherwise silent.