Infective endocarditis (IE) is a serious and life-threatening cardiac condition, most commonly caused by staphylococci, Streptococcus viridans, and enterococci. However, in special settings, IE can be caused by rare organisms. Here we present a case of IE caused by Aerococcus urinae in a 75-year-old man with a bioprosthetic aortic valve. Aerococcusurinae is a gram-positive, catalase-negative microorganism and is usually an isolate of complicated urinary tract infections in the elderly male population. Improvements in diagnostic testing including use of matrix-assisted laser desorption ionization- a time of flight mass spectrometry (MALDI-TOF MS) have played an important role in recognition of Aerococcus urinae.