This report describes a rare case of an asymptomatic myocardial abscess which was not associated with infective endocarditis but was diagnosed to be a tumor and treated by open-heart surgery. A 69-year-old patient without a history of endocarditis or myocardial infarction was submitted to invasive cardiac diagnostics after an embolic event in the brachial artery. Investigation revealed an "intracardiac tumor" and the patient subsequently underwent open-heart surgery. After cardiotomy the suggested tumor was found in the posterior wall of the left atrium adjacent to the mitral ring, appearing as a circumscribed, indurated, and plane area. After incision for biopsy, a cheesy pus emptied from a cavity. The tissue sections showed an intramural myocardial abscess. Because of the extent, location and the character of the abscess, the cavity was closed after rinsing using mattress sutures. The postoperative course was uncomplicated. This report demonstrates that in suspected cardiac tumors a myocardial abscess should be considered in any differential diagnosis despite the rarity of the event, since the diagnosis of the myocardial abscess is not an absolute indication for surgical intervention.