Constrictive pericarditis is usually a chronic inflammatory process. We encountered a case of acute constrictive pericarditis caused by infectious pericarditis in a patient receiving pericardial drainage for pericardial effusion. We performed emergency pericardiectomy and primary closure in the active phase of infection. An 82-year-old man was referred to our hospital for investigation and management of pericardial effusion. The patient was admitted, and continuous pericardial drainage was performed. After 2 days of drainage, he had fever, and after 7 days, there was purulent exudate in the drain tube. Methicillin-sensitive Staphylococcus aureus was identified by culture of the purulent exudate. Despite administration of antibiotics, he developed malaise, anorexia, and generalized edema, and he also began to suffer from dyspnea. Computed tomography demonstrated infected pericardial effusion, while a right ventricular pressure study showed a “dip and plateau” pattern. Pericardial drainage and irrigation were done via a small subxyphoid skin insicion. However, his hemodynamics did not improve and oliguria was noted. Because more extensive drainage was necessary, we performed emergency on-pump beating pericardiectomy via median sternotomy. Along with administration of antibiotics, continuous mediastinal irrigation with saline was done via mediastinal, pericardial, and chest drain tubes for 7 days after the operation. His postoperative course was relatively uneventful, and he was discharged after recovery.