Pericardial effusion is not a common finding in clinical practice. Sometimes, the pericardial effusion is a comorbidity of known underlying disease, such as end-stage renal disease, acute myocardial infarction, cardiac surgery or widespread metastatic neoplasm. When no reason is apparent, some clinical findings can be useful to establish a diagnosis. The presence of acute inflammatory signs is predictive for acute idiopathic pericarditis. Severe pericardial effusion with absence of inflammatory signs without evidence of tamponade is predictive for chronic idiopathic pericardial effusion, and tamponade without inflammatory signs for neoplastic pericardial effusion. We present a 4 years-old boy who developed tamponade and was successfully treated with surgical pericardial drainage and intravenous drugs.