A 13 year old boy presented with a one week history of cough, coryza, and shortness of breath on minimal exertion. A murmur was noted, and an echocardiogram revealed a structurally normal heart with a large pericardial effusion. A pericardial drain was inserted percutaneously and 700 ml of serous fluid was drained. The following day his clinical condition deteriorated, with tachypnoea, tachycardia, hypotension, and desaturation. A 12 lead ECG showed notably reduced voltages in all leads (panel B) compared to the admission ECG (panel A). The heart could not be visualised on transthoracic echocardiography. The chest x ray (panel C) showed wide separation of the pericardium from the heart. Aspiration of 1000 ml of air from the pericardium resulted in immediate clinical improvement. The pericardial fluid showed neutrophilia consistent with acute pericarditis. Blood and pericardial fluid cultures, Heaf test, and a cardiomyopathy screen were all negative. Antibiotics were stopped and the pericardial drain removed after four days. Further recovery was uneventful.

The presence of air in the pericardium may electrically insulate the heart, and manifest as reduced ECG voltages. Prompt aspiration is required to prevent tamponade.