A hydropneumopericardium is a rare but critical condition, which is mostly ascribed to primary infiltrative lesions from adjacent organs, pericardial infections, or trauma. Although there have been reports about pyopneumopericardium, no case of spontaneous non-purulent hydropneumopericardium has been documented in literature. We report a case of a previously healthy man of spontaneously occurred tension hydropneumopericardium complicating serofibrinous pericarditis. A surgical exploration followed by partial pericardiectomy was performed to stop cardiac tamponade and possible later constriction. Remarkably, no definite pathogenesis was identified despite surgical and laboratory investigations. The spontaneity and management of hydropneumopericardium are discussed.