A case of acute enterococcal aortic valve endocarditis is presented in which the complication of a septal myocardial abscess was diagnosed clinically and successfully treated surgically. This represents the first instance, to our knowledge, in which the preoperative diagnosis of a myocardial abscess served as the indication for emergency cardiac surgical intervention in active endocarditis with successful outcome. The diagnostic parameters permitting clinical recognition of a myocardial abscess include the development of advancing degrees of atrioventricular and bundle branch block, and the finding of pericarditis or pericardial effusion in aortic valvular infections. Two additional findings were noted in the present case: echocardiographic evidence of septal thickening, and loss of septal Q waves on the electrocardiogram. Since myocardial abscesses do not respond to medical therapy, continuous electrocardiographic monitoring and frequent echocardiographic determinations are recommended in cases of active aortic valve endocarditis to permit early diagnosis and surgical management of this complication.