Acute pericarditis may be caused by a variety of disorders. Most cases of acute pericarditis without any initial apparent cause are idiopathic, although presumably viral in origin. While staphylococcus aureus, streptococcus pneumonias and streptococcus pyogens were the predominant organisms recovered prior to 1950, gram negative bacilli, anaerobic bacteria and fungus were recovered after 1950. These changes of the etiologic diversity of acute pericarditis were related to the development and advances of cardiac surgery, antibiotics, chemotherapy for cancer and immunosuppressive treatments. It is important for the therapy of acute bacterial pericarditis to establish the proper regimen of antibiotics and to drain pericardial effusion, if needed. We report a case of acute pericarditis, caused by Klebsiella pneumoniae, an uncommon pathogen that caused purulent pericarditis with cardiac tamponade.