Recently, we met a 12 year old female patient who suffered from bacterial endocarditis and pericarditis which were complicated by patent ductus arteriosus. She was admitted to our hospital because of dyspnea, fever, headache, and generalized ache for 10 days. The initial diagnosis was bacterial endocarditis and pericarditis complicated by patent ductus arteriosus and congestive heart failure. At first, we tried to treat the patient medically with digitalis, diuretics, and massive antibiotics. On echocardiography large amount of pericardial fluid was accumulated mainly right anterior aspect and also noted a large vegetation at pulmonary valve area. With vigorous medical treatment including repeated pericardiocentesis, the patient showed no improvement. So we decided to perform pericardiectomy for elimination of the most probable septic focus. On operation, we encountered an unpredicted event, the pericardium was thickened, distended, and its surface showed pulsating which meant connecting to systemic circulation. We decided to close the operative wound and reoperate her under cardiopulmonary bypass later. On the next day, we operated her under cardiopulmonary bypass later. On the next day we operated her under cardiopulmonary bypass. The operative findings were ruptured main pulmonary artery about 1.5cm in diameter on its ventral portion, the blood from the ruptured main pulmonary artery was filled up the localized pericardial sac due to previous pericarditis. Through the ruptured main pulmonary artery, we also found 0.5cm diametered patent ductus arteriosus. With the aid of partial cardiopulmonary bypass and inserting 24F ballooned Foley catheter at aorta, pericardiectomy was performed first. After completion of the pericardiectomy, total cardiopulmonary bypass was established. With minimum pump flow [0.3L/min/m2] the PDA was closed with two Teflon-felted 4-0 Prolene interrupted sutures. The ruptured main pulmonary artery was also closed using thickened pericardium with three Teflon-felted 4-0 Prolene interrupted sutures. The operation was successful and postoperative course was uneventful. She was discharged on the 16th POD. We report this case as a very rare secondary complication of bacterial endocarditis complicated by patent ductus arteriosus.