A 33-year-old man with a history of mitral valve prolapse and a dental procedure 2 months earlier was admitted with fever. Examination revealed a holosystolic murmur at the apex, and blood cultures were positive for Streptococcus mitis. Transthoracic echocardiography revealed severe mitral regurgitation and a 25 × 18-mm mobile vegetation adherent to the anterior mitral leaflet (A). A 30-mm echodense linear structure connected the vegetation to the left atrial wall adjacent to the noncoronary sinus of Valsalva (B, green arrow; Online Video 1). Two- and 3-dimensional transesophageal echocardiography identified the structure as a false tendon (C and D, Online Video 2). The patient underwent mitral valve replacement, and surgical findings confirmed complex anterior leaflet endocarditis with an attached tan/white fibrous tissue fragment (E and F). False tendons between the mitral valve and the left atrial wall are rare and have been reported as a cause of mitral valve prolapse. To our knowledge, this is the first reported case of subacute mitral valve endocarditis involving a false tendon ( 1).